Incorrect Timing Adjustment causing heat issues?

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So talked with them this morning before I touched it. They clarified that yes the did mean misfire. They set the timing to a few degrees ATDC (somewhat arbitrarily). 10-15 degrees is out enough to cause an issue.
Adjusted it to 10 base seems fine but there is a slight miss that I haven’t tracked down. Dwell is good. Probably just the points. I have accidentally left it in the run position myself more times then I would like to admit.
 
So talked with them this morning before I touched it. They clarified that yes the did mean misfire. They set the timing to a few degrees ATDC (somewhat arbitrarily). 10-15 degrees is out enough to cause an issue.
Adjusted it to 10 base seems fine but there is a slight miss that I haven’t tracked down. Dwell is good. Probably just the points. I have accidentally left it in the run position myself more times then I would like to admit.

It would be a good idea to start with a compression and/or a cylinder leakage test to see what is going on inside.
Then: don't overlook the obvious. If you are chasing a bad running engine, make sure the tune up is good first. You could throw a $1000 worth of parts at it and still have a misfire because of a bad cracked plug or a carbon tracked cap. What ignition system do you have? Contact @halifaxhops for some quality parts if you are running a stock system. Follow up with the correct heat range of plugs and a good set of wires. No high dollar high performance ones needed, just a quality set. Then you can start chasing ghosts.
Oh and don't forget a proper valve adjustment. 273's came with solid lifter cams and need the valves adjusted from time to time.
 
it would only get this warm if it was really sitting in heavy traffic and +95F ambient. This was not the case today. (Mid to low 80s)
I also seem to be able to curb a similar problem after my first timing adjustment to the car when the two barrel was on it and subsequently after first incorrect adjustment with the four barrel.
Wiki says that you are at about 4300 ft elevation.
I didn't see a description of what exact "heat issue" you are actually speaking of, or how you are measuring your "heat issues", but
I did see "no shroud".

The lackluster power and retarded idle/low-speed timing go hand in hand. At 4300 ft, with a 273, you are gonna need all the timing you can get without hitting detonation. Also at 4300ft, with a stock engine/TC, and below ~3000 rpm, if the tires don't spin; you cannot expect much power improvement from the 4bbl. The factory 2 bbl was big enough to that point. You will get much much better result with a hi-stall TC.
While the 4bbl does make a bit of power, it follows the cam. meaning at whatever rpm the cam powerpeaks at, the 4bbl can add to it; it is not guaranteed to, if say the exhaust won't allow it. But it also means that the power does not increase like a switch, it only starts making power gradually as the cam wakes up, and only proportionally. Say your cam wakes up at 2400 and peaks at 3900. And say your 2bbl was good to 2400. Then your 4bbl will not start to make power until the engine would have run out of air with the 2bbl; say 2400. So let say's your 4bbl was good for 15 hp at 3900, and zero at 2400. That is a range of 1500rpm, and an increase of 15hp. If the power increased linearly, and it does not, but say it did; then, you could expect 1500/15hp=1hp per 100rpm. But notice that, below 2400 rpm... in this example,,,, horsepower is not increased at all.

On another note;
Rich running cools the A/F charge as the extra fuel sucks up heat during evaporation. That extra fuel goes right into the exhaust. If it finds air in there, it will catch fire and make the logs run hot. Of course the exhaust ports are part of the log-manifold system, so they too run hot, and that heat gets into the water jacket;
and like somebody said, it's a chain of events.
But the idle HAS to be slightly rich, or you will have to take other steps to keep it running, and to prevent driveability issues.
At idle, your engine will like a TON of advance, perhaps into the hi-20s or more. You can tell how much, by simply advancing the timing until the rpm stops rising, then reading the balancer.
But you cannot run it there (hi 20s) except for idling. And the reason is that at the other end at WOT/ full load wide open throttle, your engine might not want any more than 36*@3600 rpm, else it could hammer itself to death. I mean IDK your engine only you do. So then, if you set your idle timing to say 25*, you would have to build a timing curve to get just 11 more degrees by 3600. If you did that I'll bet the engine will be hammering pre-ignition holes into the tops of every piston, on every stroke....... because at say halfway to 3600 with a linear curve, she would be at ~31* by 2100, and under full power, at 4300 ft, I would not expect your engine to last very long, due to massive detonation..
However, at Part Throttle, 31* at 2100rpm will be pretty snappy after you add the Vcan in. But this too, at 4300, might be a tad much.
At 4300 ft, the MJs in that carb needs to be jetted at least two sizes smaller than at sealevel. Couple that with at least 20psi loss in cylinder pressure, and so,
the take home is this; you are gonna have to dial the timing in pretty close, for the lil 273 to come even close to what might be considered peppy.
If it was mine, I would be exploring the timing, looking for the WOT detonation lines. In the car and by myself, this could take a couple of weeks. You will need a dial-back timing light, a tachometer and lots of paper.To make this easier and much faster, I installed a dash-mounted, dial-back, timing delay box, with a range of 15*.
After the Idle Timing is close, as determined by the lack of off-idle tip-in, which is set up by the transfer slot to primary throttle opening;
after that, I would map the detonation line, and then build a distributor curve to stay under that; then I would start adding huge amounts of Vcan timing to find the PartThrottle detonation limit.
When I say huge, I mean 22/24* is about all you can modify a Mopar Vcan to get
Now to come full-circle; To get the Idle timing into the hi 20s/low 30s , as I started this post with, You can use any mix of mechanical timing plus vacuum can timing that you can imagine. Say 10mechanical and 22 Vcan, or 14 mechanical plus 18 vcan... and so on.....
but above all things, you must stay out of detonation.
 
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It would be a good idea to start with a compression and/or a cylinder leakage test to see what is going on inside.
Then: don't overlook the obvious. If you are chasing a bad running engine, make sure the tune up is good first. You could throw a $1000 worth of parts at it and still have a misfire because of a bad cracked plug or a carbon tracked cap. What ignition system do you have? Contact @halifaxhops for some quality parts if you are running a stock system. Follow up with the correct heat range of plugs and a good set of wires. No high dollar high performance ones needed, just a quality set. Then you can start chasing ghosts.
Oh and don't forget a proper valve adjustment. 273's came with solid lifter cams and need the valves adjusted from time to time.
It could mostly likely use a valve adjustment and I should do a compression test. (Off to harbor freight). Yes it is still the stock I forgot to get the tag number earlier that someone mentioned. I will get with @halifaxhops to get a setup soon.
But by miss fire it isn’t bad it is just ever so slightly noticeable at idle and you really have to be paying attention to catch it.
 
Wiki says that you are at about 4300 ft elevation.
I didn't see a description of what exact "heat issue" you are actually speaking of, or how you are measuring your "heat issues", but
I did see "no shroud".

The lackluster power and retarded idle/low-speed timing go hand in hand. At 4300 ft, with a 273, you are gonna need all the timing you can get without hitting detonation. Also at 4300ft, with a stock engine/TC, and below ~3000 rpm, if the tires don't spin; you cannot expect much power improvement from the 4bbl. The factory 2 bbl was big enough to that point. You will get much much better result with a hi-stall TC.
While the 4bbl does make a bit of power, it follows the cam. meaning at whatever rpm the cam powerpeaks at, the 4bbl can add to it; it is not guaranteed to, if say the exhaust won't allow it. But it also means that the power does not increase like a switch, it only starts making power gradually as the cam wakes up, and only proportionally. Say your cam wakes up at 2400 and peaks at 3900. And say your 2bbl was good to 2400. Then your 4bbl will not start to make power until the engine would have run out of air with the 2bbl; say 2400. So let say's your 4bbl was good for 15 hp at 3900, and zero at 2400. That is a range of 1500rpm, and an increase of 15hp. If the power increased linearly, and it does not, but say it did; then, you could expect 1500/15hp=1hp per 100rpm. But notice that, below 2400 rpm... in this example,,,, horsepower is not increased at all.

On another note;
Rich running cools the A/F charge as the extra fuel sucks up heat during evaporation. That extra fuel goes right into the exhaust. If it finds air in there, it will catch fire and make the logs run hot. Of course the exhaust ports are part of the log-manifold system, so they too run hot, and that heat gets into the water jacket;
and like somebody said, it's a chain of events.
But the idle HAS to be slightly rich, or you will have to take other steps to keep it running, and to prevent driveability issues.
At idle, your engine will like a TON of advance, perhaps into the hi-20s or more. You can tell how much, by simply advancing the timing until the rpm stops rising, then reading the balancer.
But you cannot run it there (hi 20s) except for idling. And the reason is that at the other end at WOT/ full load wide open throttle, your engine might not want any more than 36*@3600 rpm, else it could hammer itself to death. I mean IDK your engine only you do. So then, if you set your idle timing to say 25*, you would have to build a timing curve to get just 11 more degrees by 3600. If you did that I'll bet the engine will be hammering pre-ignition holes into the tops of every piston, on every stroke....... because at say halfway to 3600 with a linear curve, she would be at ~31* by 2100, and under full power, at 4300 ft, I would not expect your engine to last very long, due to massive detonation..
However, at Part Throttle, 31* at 2100rpm will be pretty snappy after you add the Vcan in. But this too, at 4300, might be a tad much.
At 4300 ft, the MJs in that carb needs to be jetted at least two sizes smaller than at sealevel. Couple that with at least 20psi loss in cylinder pressure, and so,
the take home is this; you are gonna have to dial the timing in pretty close, for the lil 273 to come even close to what might be considered peppy.
If it was mine, I would be exploring the timing, looking for the WOT detonation lines. In the car and by myself, this could take a couple of weeks. You will need a dial-back timing light, a tachometer and lots of paper.To make this easier and much faster, I installed a dash-mounted, dial-back, timing delay box, with a range of 15*.
After the Idle Timing is close, as determined by the lack of off-idle tip-in, which is set up by the transfer slot to primary throttle opening;
after that, I would map the detonation line, and then build a distributor curve to stay under that; then I would start adding huge amounts of Vcan timing to find the PartThrottle detonation limit.
When I say huge, I mean 22/24* is about all you can modify a Mopar Vcan to get
Now to come full-circle; To get the Idle timing into the hi 20s/low 30s , as I started this post with, You can use any mix of mechanical timing plus vacuum can timing that you can imagine. Say 10mechanical and 22 Vcan, or 14 mechanical plus 18 vcan... and so on.....
but above all things, you must stay out of detonation.
So heat issues are based on the stock water temp gauge. Yes I know i probably should get a set of aftermarket gauges to through under the dash. From the temp gauge my thermostat opens right at the middle line and for the most part does not get to 195 (I assume that is the next line on the stock gauges as the thermostat is 180.) The other day it was making an effort to go well above that line or what I am assuming is 195-200.
I was not expecting to much from the four barrel but the dual plane does give it a bit more down low and the AVS 2 does seem to help out a little. It is about what I expected based on our prior talks. To me it seems peppy enough as everything up here is gasping for air. (My daily is a N/A Subaru with the same factory rating.) I also haven’t driven it at any other altitude so I don’t know what I am missing.
Can you show me an example of a WOT detonation line?
(BTW) carb was rejeted properly using a gas analyzer flying in percent CO and no evidence of lean stumbles yet.
 
Can you show me an example of a WOT detonation line?

NO, but I can help you imagine one.

Suppose you set your idle-timing to 14* and you limited the Power-timing to 34*. This requires you to modify your mechanical advance mechanism so that it can only advance 34 less 14= 20*
Then suppose you installed some springs in there that were soft enough to allow the beginning of advancement to start at 1000 rpm, and it required 3400 rpm to fully advance to the max of 34*.
This is a typical performance starter tune.

So now the first thing most guys wanna figure out is how much timing the engine will tolerate before it detonates. But I don't know if most guys even know what detonation sounds like, or feels like; and typically the engine exhaust is way to loud to hear it anyway.
Furthermore; in a streeter, looking for it is crazy. Here's why;
#1, your butt-dyno cannot tell the difference between perfect timing and 2 or 3 degrees less than perfect.
#2 Who is to say your engine will want the same Power-Timing all the way from 3600 to shift-rpm?
#3 ,3600rpm with 2.76s in first gear (2.45) is about 38 mph. How often are you gonna nail it at 38 mph, and require perfect timing from there on up?
#4 How much power is actually lost, on the power peak, running 2 or 3 degrees less than perfect Power-Timing? And how much is that at 38mph?
The stock cam power-peaks at around 4000; I'd be surprised to learn that 3* less than perfect timing, equates to 6 hp. At 3600/38mph, I'd be surprised to learn of more than 2 or 3 hp. See what I mean? Hunting for perfection,this early in the game is crazy, and not worth risking engine damage to go looking for.
Therefore, set the Power-Timing limit at 34*, and call it done. To do this see note 1.

Now, earlier I talked about your typical curve being all in by 3600. You need to map your current curve to have a starting point; see note 2. If your curve is done by 3000, don't sweat it. Just don't mash the gas until 3600 for testing purposes. I am trying to save your engine,We'll get to sub-3600 in just a bit.
Having done that,Your Power-timing is now set, and it behooves you to verify that this is not too much. see note 3.
Having done that; you now test all the rpms from stall to 3600, with the existing curve. If you hear detonation, see note 4. If you do not hear detonation, see note5



Note 1.
Just rev it up until the the D stops advancing, and move the Distributor to change the timing to 34* from whatever it was. This will usually occur close to 3600 but could go as high as 4200.
Note 2
Ok now let's make a map. Grab a sheet of graph paper, and draw a giant L on it, using the 4th line from the edges. The vertical line will be calibrated in degrees, and the horizontal in rpm. Start in the corner as 0-0. Upwards you need about 40 degrees. and sideways you need about 4000 rpm.
Where 3600 and 34 degrees meet , you put your first data point.
Note3
roadtest time! take the warmed up engine to 3500 in second gear. We are gonna use the wind for a load tester cuz that's all we got. If this is more than the speed limit with your gears and tires, STOP! Start over in first gear. Now, back to 3500. Slam the pedal down, and listen carefully. When she gets to 4400 stop the test. If you did not hear detonation, and you know what it sounds like, and your combo is actually quiet enough that you are able to hear the engine; Great, call it done for now. Try it several times cuz it's just so much fun, er, I mean, to be sure.
Note 4
Note 5

more coming, but I got some stuff to do now
 
NO, but I can help you imagine one.

Suppose you set your idle-timing to 14* and you limited the Power-timing to 34*. This requires you to modify your mechanical advance mechanism so that it can only advance 34 less 14= 20*
Then suppose you installed some springs in there that were soft enough to allow the beginning of advancement to start at 1000 rpm, and it required 3400 rpm to fully advance to the max of 34*.
This is a typical performance starter tune.

So now the first thing most guys wanna figure out is how much timing the engine will tolerate before it detonates. But I don't know if most guys even know what detonation sounds like, or feels like; and typically the engine exhaust is way to loud to hear it anyway.
Furthermore; in a streeter, looking for it is crazy. Here's why;
#1, your butt-dyno cannot tell the difference between perfect timing and 2 or 3 degrees less than perfect.
#2 Who is to say your engine will want the same Power-Timing all the way from 3600 to shift-rpm?
#3 ,3600rpm with 2.76s in first gear (2.45) is about 38 mph. How often are you gonna nail it at 38 mph, and require perfect timing from there on up?
#4 How much power is actually lost, on the power peak, running 2 or 3 degrees less than perfect Power-Timing? And how much is that at 38mph?
The stock cam power-peaks at around 4000; I'd be surprised to learn that 3* less than perfect timing, equates to 6 hp. At 3600/38mph, I'd be surprised to learn of more than 2 or 3 hp. See what I mean? Hunting for perfection,this early in the game is crazy, and not worth risking engine damage to go looking for.
Therefore, set the Power-Timing limit at 34*, and call it done. To do this see note 1.

Now, earlier I talked about your typical curve being all in by 3600. You need to map your current curve to have a starting point; see note 2. If your curve is done by 3000, don't sweat it. Just don't mash the gas until 3600 for testing purposes. I am trying to save your engine,We'll get to sub-3600 in just a bit.
Having done that,Your Power-timing is now set, and it behooves you to verify that this is not too much. see note 3.
Having done that; you now test all the rpms from stall to 3600, with the existing curve. If you hear detonation, see note 4. If you do not hear detonation, see note5



Note 1.
Just rev it up until the the D stops advancing, and move the Distributor to change the timing to 34* from whatever it was. This will usually occur close to 3600 but could go as high as 4200.
Note 2
Ok now let's make a map. Grab a sheet of graph paper, and draw a giant L on it, using the 4th line from the edges. The vertical line will be calibrated in degrees, and the horizontal in rpm. Start in the corner as 0-0. Upwards you need about 40 degrees. and sideways you need about 4000 rpm.
Where 3600 and 34 degrees meet , you put your first data point.
Note3
roadtest time! take the warmed up engine to 3500 in second gear. We are gonna use the wind for a load tester cuz that's all we got. If this is more than the speed limit with your gears and tires, STOP! Start over in first gear. Now, back to 3500. Slam the pedal down, and listen carefully. When she gets to 4400 stop the test. If you did not hear detonation, and you know what it sounds like, and your combo is actually quiet enough that you are able to hear the engine; Great, call it done for now. Try it several times cuz it's just so much fun, er, I mean, to be sure.
Note 4
Note 5

more coming, but I got some stuff to do now
I wasn’t worried about going for perfection and getting that last few hp out of it. To me as it is is fine. Especially since there is no drag strip around here. Only reason why it went to the shop for the tuning is I knew it would be rich out of the box but don’t have the equipment or to determine exactly how much fuel needed to be pulled out.
It will also start snowing here before I know it so I don’t want to do to many projects making it out of service. I appreciate your explanation though.
 
Did the shop have a chassis dyno that can be loaded?
Or an old emissions dyno?
Otherwise its just guess work.
Consider it ballparked, but not tuned.
AFR should not be targetted except for emissions reasons and when given factory specs for a particular condition (usually idle).

The first thing to get correct is the timing. Then work on fueling.
On a hot rodded engine this can be an iterative process of tuning timing and caburation for each of the steady state conditions.
Since this is fairly factory, I strongly suggest going with the factory timing curve. They put a lot of effort into testing and tweaking for best efficiency under all conditions. So that will save a lot of time and effort on your part.
For '67, which is the earliest book I have, the 273 4 bbl has a different timing curve than the 2 bbl. But it also had a different cam and compression.
My suggestion for this fall is that IF the distributor is the original, go with it. Set the initial at the factory recommended as you have. Tweak it slightly (2 degrees) if there is a reason (such as pinging under wide open throttle). One caveat: If the idle speed is much higher than the factory spec, this can throw off the entire timing curve. Second caveat: The initial should be set with the vacuum advance disconnected and the hose connecting to the vacuum source plugged. Golf tee makes a good plug. That may seem obvious but less and less people seem to know this. I know I had to be told this 30 years ago. In the newer cars (70s and 80s) the factory tune up info usually states this but I don't know if it explains that in the '65 shop manual or not.

Next.
A compression check was suggested. That's a good idea but a fair amount of work. I would probably pop the distributor cap and look at the points next. Maybe run a piece of paper between them. I know its pain leaning across the fender, but that's what I'd do next. Then probably look at the spark plugs for any obvious differences. You're going to have to pull them anyway for the comrpession check.
Where the compression check is probably leading is to valve adjustment. Some people might go right to that, then do a compression check afterwords if needed.
Do whatever fits your skills, timeline and preferences.

Back to the fuel mixture.
Tune for Performance.
Performance defined as power, torque and engine efficiency.
This requires systematic trials

Start at the idle and work up.
Idle and off idle are your foundations.
Performance here is going to be revealed by how little throttle is needed to keep the rpms with load.
(manual) to get into first gear without stalling.
(automatic) lose the least rpm when placed in drive. Alternatively have the best vacuum at a given rpm in drive.
Adjust the idle mixture screws 1/8 turn at a time toward lean (clockwise) until the rpms fall off a little.
Adjust them back from that point 1/8 a turn. Check vacuum and or rpm going into gear with your foot on the brake.
You can try another 1/8 turn richer and see if there is any improvement. etc.
If the idle rpms went out of range (higher) with the new mixture, then you can idle speed screw slightly (transfer slots), and check repeat the above excercise.

Next confirm off-idle has good performance by very slowly accelerating from stop with no hesitation. This test minimizes the role of the pump shot and focus on the idle circuit's begining of transition.
If that's good, then test more normal acceleration (for public streets) from stop to make sure the pump shot is not too much or too little for this basic job.

Then you can test out steady driving at various speeds. The fuel ratio at steady interstate highway speeds is determined by main jet and the rods. Steady cruising on local highways
(up to 50 or 60 mph) will still be at least partially using the "idle circuit". It shou;ld be really called low throttle circuit but too late to change that. LOL.
If its too lean while cruising, it will surge. Slow down and take it back to garage. With the Carter type design the high speed cruising restriction is based on the rod and jet combination. Either change the rod or the combination rod and jet. For Edelbrock carbs, edelbrock provides a chart each model showing which combination is needed to make it richer at cruising from whatever combination is in that carb now.

If you have access to the strip or dyno you can test wide open throttle in top gear. AFR is controlled by the jets plus the step up circuit.
If the tune up shop ahad a chassis dyno, that may be what they did for jetting.
All the above tests are effected by timing. If you change timing at a given rpm and condition, then retest before change fuel mixture for that condition.

A good overview of the various circuits in a Carter type carb is in the 1966 and 1970 Chrysler Master Tech "Carburetor Fundementals"
Master Technician Service Conference - Chrysler's Training for Mechanics
A little more about AFR for different conditions is this post
Wideband
 
Did the shop have a chassis dyno that can be loaded?
Or an old emissions dyno?
Otherwise its just guess work.
Consider it ballparked, but not tuned.
AFR should not be targetted except for emissions reasons and when given factory specs for a particular condition (usually idle).

The first thing to get correct is the timing. Then work on fueling.
On a hot rodded engine this can be an iterative process of tuning timing and caburation for each of the steady state conditions.
Since this is fairly factory, I strongly suggest going with the factory timing curve. They put a lot of effort into testing and tweaking for best efficiency under all conditions. So that will save a lot of time and effort on your part.
For '67, which is the earliest book I have, the 273 4 bbl has a different timing curve than the 2 bbl. But it also had a different cam and compression.
My suggestion for this fall is that IF the distributor is the original, go with it. Set the initial at the factory recommended as you have. Tweak it slightly (2 degrees) if there is a reason (such as pinging under wide open throttle). One caveat: If the idle speed is much higher than the factory spec, this can throw off the entire timing curve. Second caveat: The initial should be set with the vacuum advance disconnected and the hose connecting to the vacuum source plugged. Golf tee makes a good plug. That may seem obvious but less and less people seem to know this. I know I had to be told this 30 years ago. In the newer cars (70s and 80s) the factory tune up info usually states this but I don't know if it explains that in the '65 shop manual or not.

Next.
A compression check was suggested. That's a good idea but a fair amount of work. I would probably pop the distributor cap and look at the points next. Maybe run a piece of paper between them. I know its pain leaning across the fender, but that's what I'd do next. Then probably look at the spark plugs for any obvious differences. You're going to have to pull them anyway for the comrpession check.
Where the compression check is probably leading is to valve adjustment. Some people might go right to that, then do a compression check afterwords if needed.
Do whatever fits your skills, timeline and preferences.

Back to the fuel mixture.
Tune for Performance.
Performance defined as power, torque and engine efficiency.
This requires systematic trials

Start at the idle and work up.
Idle and off idle are your foundations.
Performance here is going to be revealed by how little throttle is needed to keep the rpms with load.
(manual) to get into first gear without stalling.
(automatic) lose the least rpm when placed in drive. Alternatively have the best vacuum at a given rpm in drive.
Adjust the idle mixture screws 1/8 turn at a time toward lean (clockwise) until the rpms fall off a little.
Adjust them back from that point 1/8 a turn. Check vacuum and or rpm going into gear with your foot on the brake.
You can try another 1/8 turn richer and see if there is any improvement. etc.
If the idle rpms went out of range (higher) with the new mixture, then you can idle speed screw slightly (transfer slots), and check repeat the above excercise.

Next confirm off-idle has good performance by very slowly accelerating from stop with no hesitation. This test minimizes the role of the pump shot and focus on the idle circuit's begining of transition.
If that's good, then test more normal acceleration (for public streets) from stop to make sure the pump shot is not too much or too little for this basic job.

Then you can test out steady driving at various speeds. The fuel ratio at steady interstate highway speeds is determined by main jet and the rods. Steady cruising on local highways
(up to 50 or 60 mph) will still be at least partially using the "idle circuit". It shou;ld be really called low throttle circuit but too late to change that. LOL.
If its too lean while cruising, it will surge. Slow down and take it back to garage. With the Carter type design the high speed cruising restriction is based on the rod and jet combination. Either change the rod or the combination rod and jet. For Edelbrock carbs, edelbrock provides a chart each model showing which combination is needed to make it richer at cruising from whatever combination is in that carb now.

If you have access to the strip or dyno you can test wide open throttle in top gear. AFR is controlled by the jets plus the step up circuit.
If the tune up shop ahad a chassis dyno, that may be what they did for jetting.
All the above tests are effected by timing. If you change timing at a given rpm and condition, then retest before change fuel mixture for that condition.

A good overview of the various circuits in a Carter type carb is in the 1966 and 1970 Chrysler Master Tech "Carburetor Fundementals"
Master Technician Service Conference - Chrysler's Training for Mechanics
A little more about AFR for different conditions is this post
Wideband
If you told me about two months ago the timing deal would actually have been news. I am new to the carburetor world but not tuning.
For the AFR, I am used to targeting it for emissions fuel economy and enriching it for power with fuel maps for fuel injected cars. Is their the same no but out of the box any carb at 4500 ft elevation is going to be rich. So it may have been an emissions dyno but with out an AFR gauge to monitor it myself and make pulls etc. there guess is better then mine. Idle speed is right around factory recommendations so I should be good with the base timing. I could probably get away with an extra two degrees or so with the elevation or maybe not. Highest octane we get up here is 91 which at altitude is our equivalent to 93. I will play around with it eventually but for now with no tracks and no intention of racing she is a good cruiser with no knock.
Come spring it will need the bottom resealed and with the way the exhaust was done by the prior owner it will need to be cut. So I will end up going to a new exhaust system of sorts. (I know what AJ will say that headers won’t make a difference but now way these factory 273 manifolds can do the motor any favors.) so it will get a wide band setup at that point and I will be better able to dial it in myself.
 
I am used to targeting it for emissions fuel economy and enriching it for power with fuel maps for fuel injected cars. Is their the same no but out of the box any carb at 4500 ft elevation is going to be rich
Carter carbs have a stepped rods that change the effective jet size due to various vacuum and throttle positions.

Compared to EFI it is from the stone ages, but it worked fine for 100 years.

A little rich is better than a little lean IMHO
 
Carter carbs have a stepped rods that change the effective jet size due to various vacuum and throttle positions.

Compared to EFI it is from the stone ages, but it worked fine for 100 years.

A little rich is better than a little lean IMHO
Agreed but at 4500 ft it was really rich out of the box.
 
I brought me 67 273 2bbl from CA to northern CO. (5000 feet). I assumed the same and rejected my carb. Ran like crap. Misfiring etc.

Discovered the 2 steps lean was causing lean misfire. I put the OEM jets back in and no more issue. Turns out 5000 feet is not that high.
 
I brought me 67 273 2bbl from CA to northern CO. (5000 feet). I assumed the same and rejected my carb. Ran like crap. Misfiring etc.

Discovered the 2 steps lean was causing lean misfire. I put the OEM jets back in and no more issue. Turns out 5000 feet is not that high.
Did you try just one step lean?
 
I'm only against headers when the cost to benefit ratio comes up short.
Headers have several operating modes, and by themselves, on a lo-perf engine, offer very little benefit in the rpm and speed range, of SOME combos.

The stock 2bbl cam IIRC is a 240/248/111+4
That means the overlap at .008 is just ~22degrees; not enough for the headers to make any meaningful power with, and even if it did, it wouldn't be until way up in the rpm.
So that leaves just inertial tuning. And this also works lock-step with rpm, but more so with throttle opening, and even more so with Effective cylinder pressure. That means, for a cruiser, operating below say 2800 and almost always at low throttle openings, nothing significant is going on; they are basically acting just as a large, free-flowing exhaust system, reservoir.
Now if you have 2.73 rear gears, then 2800rpm in first gear is ~33mph; so below 33mph, the headers are not helping you much if at all. If the tires don't spin, then the same goes for the 4bbl; the stock 2bbl is plenty big enough at 2800. If the engine can only pull 230 cfm at 2800; then the engine does not care at 2800 rpm how many barrels are feeding it, it will make no more significant power with 8 as with 2.

At or below 2800, the only things that can liven up your already-built, normally-aspirated, stock-cammed 273 engine, are; Stall-speed, and gears.
This is because at the stock stall, at WOT, the 273 make very little power, and the 2.73 gears keep the engine down in the low-power zone all the way to 2800=33mph
Just as an example, 5.38s would hit 2800at 17mph.

But the bigger deal is the stall. I don't know what your combo currently stalls at, but I would be surprised if it was higher than 2000. At 2000, I would not be surprised if your engine made only 130ftlbs of torque at sealevel. that's ~50hp. But by 2800, she might be up to 100hp. So if you installed a 2800TC, you would be looking at about doubling your available power at zero mph.This is far far more effective than headers or a 4bbl.

Now lets look at gears. Mopar's line up looks like
2.76-2.94-3.23-3.55-3.73-3.91-4.10-4.30 the splits from 2.76 to 3.55 are about 9%, and thereafter are about 4.75%.
What that means to you is, whatever torque is coming out of your transmission, by the time it gets into the rear axles, it will be multiplied by whatever your rear ratio is, or increased by the percentage steps.

Your A904 has ratios of 2.45-1.45-1.00 .. So whatever torque is coming out of the TC, the trans will multiply it by one of these ratios.

Your TC has a hydraulic multiplier inside it that multiplies whatever is coming out of the crank to a higher number that is constantly varying between about 1.8 to 1.10 depending on; LOAD/throttle opening, rpm, and roadspeed.

At 2000, earlier I said your engine might be making 50hp. This is equivalent to 131 ftlbs. So at ZERO mph, that 273 slamming 131ftlbs into the TC.
Out of the TC might be coming 131 x1.8=236 ftlbs.
After the trans; 236 x2.45 (first gear)=579 ftlbs.
After the rear gears; 579 x2.76=1598ftlbs, and as you may know, this is at sealevel, and it is a pretty small number.

Lets work it out with a 2800TC and 3.55 gears.. First I convert the 100hp to ftlbs at 2800 and I get (100 x5250)/2800= 188. then ;
188 x1.8 x2.45 x3.55=2943.. This close to double what what you might currently have and, is high enough to start the tires spinning. But recall that this is at zero mph. As the car picks up speed, the TC multiplier is gonna roll back closer to it's final multiplier which at WOT might eventually diminish to 1.1. But at say 3600, I'm imagining he torque has dropped to 165, and the multiplier to perhaps 1.4, so now, out the axles looks like
165 x1.4 x2.45 x3.55= 2009 ftlbs. So unless your tires are skinny, they will not likely still be spinning. That's ok tho, because 2009 is still ~26% better than 1598.
Lets go to 4200 about where the stock cam peaks . I'm imagining 160 ftlbs ans 1.3 Multiplier so
160 x1.3 x2.45 x3.55= 1809, still over 13% higher than the best current number.

If you had an A999 with ratios of 2.74-1.54-1.00, then it would be 2.74/2.45= plus 11.84% higher, so; 2023@ 4200; which is a really good number for a streeter.
But Ima thinking, with the A999 you could roll back to 3.23s for 3.23/3.55= 1840. And now you are cruising 65=2670@ zero-slip, in loc-up.And your starter gear is 2.74 x3.23=8.85, pretty good for a streeter.

So where do headers and a 4bbl play into this?
Well, because we are now at ~100hp @2800, the 4bbl could begin opening about here. And the power is gonna peak at say 4000, So we have 1200 rpm, and the power increase will go from zero @2800 to say; I'm guessing, 12hp at 4000, so that looks like 1hp every 100 rpm and the headers might do the same. Well that might be a lil generous for the stock cam.
But the point I wanna make is that the headers and 4bbl together will not make half the poer that the Hi-stall did, and they are doing at the top of the powerband;
Whereas the stall and gears are doing at the very bottom, as soon as you nail the gas.

Now hang on a sec; I just gotta say; 4500rpm with an A904/3.55s is now 29 mph. With the A999/3.55s it is 26mph
whereas with the current A904/2.76s (guessing that is what you have) 4500 is 37mph.
So the 3.55s have blasted thru first gear at least 12 mph sooner. That means the engine has delivered it's power that much quicker, which means it took less time to get to 29 mph, and it will also take less time to get thru second,for the same reason.

And; we haven't even opened up the engine.
 
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I'm only against headers when the cost to benefit ratio comes up short.
Headers have several operating modes, and by themselves, on a lo-perf engine, offer very little benefit in the rpm and speed range, of SOME combos.

The stock 2bbl cam IIRC is a 240/248/111+4
That means the overlap at .008 is just ~22degrees; not enough for the headers to make any meaningful power with, and even if it did, it wouldn't be until way up in the rpm.
So that leaves just inertial tuning. And this also works lock-step with rpm, but more so with throttle opening, and even more so with Effective cylinder pressure. That means, for a cruiser, operating below say 2800 and almost always at low throttle openings, nothing significant is going on; they are basically acting just as a large, free-flowing exhaust system, reservoir.
Now if you have 2.73 rear gears, then 2800rpm in first gear is ~33mph; so below 33mph, the headers are not helping you much if at all. If the tires don't spin, then the same goes for the 4bbl; the stock 2bbl is plenty big enough at 2800. If the engine can only pull 230 cfm at 2800; then the engine does not care at 2800 rpm how many barrels are feeding it, it will make no more significant power with 8 as with 2.

At or below 2800, the only things that can liven up your already-built, normally-aspirated, stock-cammed 273 engine, are; Stall-speed, and gears.
This is because at the stock stall, at WOT, the 273 make very little power, and the 2.73 gears keep the engine down in the low-power zone all the way to 2800=33mph
Just as an example, 5.38s would hit 2800at 17mph.

But the bigger deal is the stall. I don't know what your combo currently stalls at, but I would be surprised if it was higher than 2000. At 2000, I would not be surprised if your engine made only 130ftlbs of torque at sealevel. that's ~50hp. But by 2800, she might be up to 100hp. So if you installed a 2800TC, you would be looking at about doubling your available power at zero mph.This is far far more effective than headers or a 4bbl.

Now lets look at gears. Mopar's line up looks like
2.76-2.94-3.23-3.55-3.73-3.91-4.10-4.30 the splits from 2.76 to 3.55 are about 9%, and thereafter are about 4.75%.
What that means to you is, whatever torque is coming out of your transmission, by the time it gets into the rear axles, it will be multiplied by whatever your rear ratio is, or increased by the percentage steps.

Your A904 has ratios of 2.45-1.45-1.00 .. So whatever torque is coming out of the TC, the trans will multiply it by one of these ratios.

Your TC has a hydraulic multiplier inside it that multiplies whatever is coming out of the crank to a higher number that is constantly varying between about 1.8 to 1.10 depending on; LOAD/throttle opening, rpm, and roadspeed.

At 2000, earlier I said your engine might be making 50hp. This is equivalent to 131 ftlbs. So at ZERO mph, that 273 slamming 131ftlbs into the TC.
Out of the TC might be coming 131 x1.8=236 ftlbs.
After the trans; 236 x2.45 (first gear)=579 ftlbs.
After the rear gears; 579 x2.76=1598ftlbs, and as you may know, this is at sealevel, and it is a pretty small number.

Lets work it out with a 2800TC and 3.55 gears.. First I convert the 100hp to ftlbs at 2800 and I get (100 x5250)/2800= 188. then ;
188 x1.8 x2.45 x3.55=2943.. This close to double what what you might currently have and, is high enough to start the tires spinning. But recall that this is at zero mph. As the car picks up speed, the TC multiplier is gonna roll back closer to it's final multiplier which at WOT might eventually diminish to 1.1. But at say 3600, I'm imagining he torque has dropped to 165, and the multiplier to perhaps 1.4, so now, out the axles looks like
165 x1.4 x2.45 x3.55= 2009 ftlbs. So unless your tires are skinny, they will not likely still be spinning. That's ok tho, because 2009 is still ~26% better than 1598.
Lets go to 4200 about where the stock cam peaks . I'm imagining 160 ftlbs ans 1.3 Multiplier so
160 x1.3 x2.45 x3.55= 1809, still over 13% higher than the best current number.

If you had an A999 with ratios of 2.74-1.54-1.00, then it would be 2.74/2.45= plus 11.84% higher, so; 2023@ 4200; which is a really good number for a streeter.
But Ima thinking, with the A999 you could roll back to 3.23s for 3.23/3.55= 1840. And now you are cruising 65=2670@ zero-slip, in loc-up.And your starter gear is 2.74 x3.23=8.85, pretty good for a streeter.

So where do headers and a 4bbl play into this?
Well, because we are now at ~100hp @2800, the 4bbl could begin opening about here. And the power is gonna peak at say 4000, So we have 1200 rpm, and the power increase will go from zero @2800 to say; I'm guessing, 12hp at 4000, so that looks like 1hp every 100 rpm and the headers might do the same. Well that might be a lil generous for the stock cam.
But the point I wanna make is that the headers and 4bbl together will not make half the poer that the Hi-stall did, and they are doing at the top of the powerband;
Whereas the stall and gears are doing at the very bottom, as soon as you nail the gas.

Now hang on a sec; I just gotta say; 4500rpm with an A904/3.55s is now 29 mph. With the A999/3.55s it is 26mph
whereas with the current A904/2.76s (guessing that is what you have) 4500 is 37mph.
So the 3.55s have blasted thru first gear at least 12 mph sooner. That means the engine has delivered it's power that much quicker, which means it took less time to get to 29 mph, and it will also take less time to get thru second,for the same reason.

And; we haven't even opened up the engine.
I actually ordered a set of 3.55s and then returned them when I got a $600 quote to install them. So 3.55s are likely in the future. I also am not sure that I would change the TC out unless I was going to a later year trans with OD and a lockup converter.
The exhaust situation is currently just strange because the prior owner put duals on it but they seem small and the left the factory Y-pipe but just didn’t merge it.
 
I think it might be. I brought it to them set around 10 degrees base timing. (Pretty standard.) they apparently adjusted it because it was “misfiring” at around 2500 rpm...? Which I would understand if it was knocking you would retard the timing but a miss fire is a separate ignition issue that also needs to be addressed. Bad ground etc.
It also feels like l what little power existed is gone. It seemed to get hot enough on the very last bit of my drive to give either a big back fire or a singular bad knock. It also seems to skip a beet every few rotations at idle which would be more down the timing misfire road.
Is it possible that I need a new cap, rotor and condenser if the accidental left the key in the run position while off?
You just cant find people that know how to work on cars anymore:) There are a couple of ways to set timing,setting at 10 initial is one,and setting for 32-36 full out is another. But yes, the "misfire" could be anything...after the electrical parts are ruled out,it could be mechanical. probably a bad wire though, its tough to get good parts these days:)
 
I'm only against headers when the cost to benefit ratio comes up short.
Headers have several operating modes, and by themselves, on a lo-perf engine, offer very little benefit in the rpm and speed range, of SOME combos.

The stock 2bbl cam IIRC is a 240/248/111+4
That means the overlap at .008 is just ~22degrees; not enough for the headers to make any meaningful power with, and even if it did, it wouldn't be until way up in the rpm.
So that leaves just inertial tuning. And this also works lock-step with rpm, but more so with throttle opening, and even more so with Effective cylinder pressure. That means, for a cruiser, operating below say 2800 and almost always at low throttle openings, nothing significant is going on; they are basically acting just as a large, free-flowing exhaust system, reservoir.
Now if you have 2.73 rear gears, then 2800rpm in first gear is ~33mph; so below 33mph, the headers are not helping you much if at all. If the tires don't spin, then the same goes for the 4bbl; the stock 2bbl is plenty big enough at 2800. If the engine can only pull 230 cfm at 2800; then the engine does not care at 2800 rpm how many barrels are feeding it, it will make no more significant power with 8 as with 2.

At or below 2800, the only things that can liven up your already-built, normally-aspirated, stock-cammed 273 engine, are; Stall-speed, and gears.
This is because at the stock stall, at WOT, the 273 make very little power, and the 2.73 gears keep the engine down in the low-power zone all the way to 2800=33mph
Just as an example, 5.38s would hit 2800at 17mph.

But the bigger deal is the stall. I don't know what your combo currently stalls at, but I would be surprised if it was higher than 2000. At 2000, I would not be surprised if your engine made only 130ftlbs of torque at sealevel. that's ~50hp. But by 2800, she might be up to 100hp. So if you installed a 2800TC, you would be looking at about doubling your available power at zero mph.This is far far more effective than headers or a 4bbl.

Now lets look at gears. Mopar's line up looks like
2.76-2.94-3.23-3.55-3.73-3.91-4.10-4.30 the splits from 2.76 to 3.55 are about 9%, and thereafter are about 4.75%.
What that means to you is, whatever torque is coming out of your transmission, by the time it gets into the rear axles, it will be multiplied by whatever your rear ratio is, or increased by the percentage steps.

Your A904 has ratios of 2.45-1.45-1.00 .. So whatever torque is coming out of the TC, the trans will multiply it by one of these ratios.

Your TC has a hydraulic multiplier inside it that multiplies whatever is coming out of the crank to a higher number that is constantly varying between about 1.8 to 1.10 depending on; LOAD/throttle opening, rpm, and roadspeed.

At 2000, earlier I said your engine might be making 50hp. This is equivalent to 131 ftlbs. So at ZERO mph, that 273 slamming 131ftlbs into the TC.
Out of the TC might be coming 131 x1.8=236 ftlbs.
After the trans; 236 x2.45 (first gear)=579 ftlbs.
After the rear gears; 579 x2.76=1598ftlbs, and as you may know, this is at sealevel, and it is a pretty small number.

Lets work it out with a 2800TC and 3.55 gears.. First I convert the 100hp to ftlbs at 2800 and I get (100 x5250)/2800= 188. then ;
188 x1.8 x2.45 x3.55=2943.. This close to double what what you might currently have and, is high enough to start the tires spinning. But recall that this is at zero mph. As the car picks up speed, the TC multiplier is gonna roll back closer to it's final multiplier which at WOT might eventually diminish to 1.1. But at say 3600, I'm imagining he torque has dropped to 165, and the multiplier to perhaps 1.4, so now, out the axles looks like
165 x1.4 x2.45 x3.55= 2009 ftlbs. So unless your tires are skinny, they will not likely still be spinning. That's ok tho, because 2009 is still ~26% better than 1598.
Lets go to 4200 about where the stock cam peaks . I'm imagining 160 ftlbs ans 1.3 Multiplier so
160 x1.3 x2.45 x3.55= 1809, still over 13% higher than the best current number.

If you had an A999 with ratios of 2.74-1.54-1.00, then it would be 2.74/2.45= plus 11.84% higher, so; 2023@ 4200; which is a really good number for a streeter.
But Ima thinking, with the A999 you could roll back to 3.23s for 3.23/3.55= 1840. And now you are cruising 65=2670@ zero-slip, in loc-up.And your starter gear is 2.74 x3.23=8.85, pretty good for a streeter.

So where do headers and a 4bbl play into this?
Well, because we are now at ~100hp @2800, the 4bbl could begin opening about here. And the power is gonna peak at say 4000, So we have 1200 rpm, and the power increase will go from zero @2800 to say; I'm guessing, 12hp at 4000, so that looks like 1hp every 100 rpm and the headers might do the same. Well that might be a lil generous for the stock cam.
But the point I wanna make is that the headers and 4bbl together will not make half the poer that the Hi-stall did, and they are doing at the top of the powerband;
Whereas the stall and gears are doing at the very bottom, as soon as you nail the gas.

Now hang on a sec; I just gotta say; 4500rpm with an A904/3.55s is now 29 mph. With the A999/3.55s it is 26mph
whereas with the current A904/2.76s (guessing that is what you have) 4500 is 37mph.
So the 3.55s have blasted thru first gear at least 12 mph sooner. That means the engine has delivered it's power that much quicker, which means it took less time to get to 29 mph, and it will also take less time to get thru second,for the same reason.

And; we haven't even opened up the engine.
Funny you say, when I was a young man, it had to be headers an 2.5 all the way back, I am older now and put stock manifolds/ exhaust on my 340 Swinger. I am not racing it so...I always wanted it back to "stock" or close to stock. It isnt cheap though...parts are crazy these days.
 
You just cant find people that know how to work on cars anymore:) There are a couple of ways to set timing,setting at 10 initial is one,and setting for 32-36 full out is another. But yes, the "misfire" could be anything...after the electrical parts are ruled out,it could be mechanical. probably a bad wire though, its tough to get good parts these days:)


You have to set both initial and total. They are not separate.
 
If I had a small engine, and an automatic, and I wanted a lil more oomph off the line with my street car; then
the very first thing I would do is install a higher stall TC, without question I always put my 2800 in there. I have had that 2800 since 1978, and it followed me thru every smoggerteen I have ever owned. It is well worth the afternoon of work to get it up there.

BTW1
If I could get $600 for a couple of hours work. I would have to hang myself; I just couldn't live with myself; that is outrageous ....... unless it includes a complete re-bearing. and a SG tune-up..
BTW2
As to exhaust; A lo-po 273 automatic with 2.76 gears could push it's exhaust thru a straight straw to about 20 mph, in first gear at WOT. Ok that's a bit of an exaggeration, But as we have already seen, with a 2000 stall, the engine might be making 50hp gross down there, so maybe 43 net. For that, a single 1.88 pipe is already more than it needs.If you floor it at 33mph, so it goes down into first, the engine will buzz up to ~4000rpm, now at or near peak power, which IIRC was 180gross when new, so say 160 net, and now over 50 years later, maybe 150hp net . that engine will not need much exhaust system to pass that amount of power, which is at sealevel! not 4300ft elevation. :(
But this is something you can easily test with a pressure gauge. Just Tee into the worst looking pipe somewhere convenient between the Y and the muffler,and run a hose up into the cab, plumbed to a very low, wide-sweep, pressure gauge. Now take it for a spin. I like to see less than 2psi for a performance car, but for yours 3.5 to 4psi under worst case, IMO, would be acceptable.
But if the Y has been hacked for duals, I would pressure test it also, cuz I have seen some crazy hack Y mods.
 
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If I had a small engine, and an automatic, and I wanted a lil more oomph off the line with my street car; then
the very first thing I would do is install a higher stall TC, without question I always put my 2800 in there. I have had that 2800 since 1978, and it followed me thru every smoggerteen I have ever owned. It is well worth the afternoon of work to get it up there.

BTW1
If I could get $600 for a couple of hours work. I would have to hang myself; I just couldn't live with myself; that is outrageous ....... unless it includes a complete re-bearing. and a SG tune-up..
BTW2
As to exhaust; A lo-po 273 automatic with 2.76 gears could push it's exhaust thru a straight straw to about 20 mph, in first gear at WOT. Ok that's a bit of an exaggeration, But as we have already seen, with a 2000 stall, the engine might be making 50hp gross down there, so maybe 43 net. For that, a single 1.88 pipe is already more than it needs.If you floor it at 33mph, so it goes down into first, the engine will buzz up to ~4000rpm, now at or near peak power, which IIRC was 180gross when new, so say 160 net, and now over 50 years later, maybe 150hp net . that engine will not need much exhaust system to pass that amount of power, which is at sealevel! not 4300ft elevation. :(
But this is something you can easily test with a pressure gauge. Just Tee into the worst looking pipe somewhere convenient between the Y and the muffler,and run a hose up into the cab, plumbed to a very low, wide-sweep, pressure gauge. Now take it for a spin. I like to see less than 2psi for a performance car, but for yours 3.5 to 4psi under worst case, IMO, would be acceptable.
But if the Y has been hacked for duals, I would pressure test it also, cuz I have seen some crazy hack Y mods.
The Y is Hacked right where the would merge. So the passenger side comes over like it would merge but just doesn't. Then a pipe runs back over to the drivers side. It is a strange setup and headers or not I have to cut the thing to drop the pan. So either modify the trans cross member or put in a Hi-PO Y pipe. Heck I have even though of using the Y pipe to act as an X-pipe of sorts and then branch it back out because it currently does not have any crossover.
 
I think it might be. I brought it to them set around 10 degrees base timing. (Pretty standard.) they apparently adjusted it because it was “misfiring” at around 2500 rpm...? Which I would understand if it was knocking you would retard the timing but a miss fire is a separate ignition issue that also needs to be addressed. Bad ground etc.
It also feels like l what little power existed is gone. It seemed to get hot enough on the very last bit of my drive to give either a big back fire or a singular bad knock. It also seems to skip a beet every few rotations at idle which would be more down the timing misfire road.
Is it possible that I need a new cap, rotor and condenser if the accidental left the key in the run position while off?
IMO it sounds like you need to find a new shop that is competent that you can trust. Or better yet dig in and start doing your own tuning, it's not difficult if you follow the basic's.
 
IMO it sounds like you need to find a new shop that is competent that you can trust. Or better yet dig in and start doing your own tuning, it's not difficult if you follow the basic's.
I agree but I am limited in tools and space. (Working out of a parking garage in my apartment.) Anything that seems like it might need to be in the air for a while has to go somewhere else. There are rules that the car cannot be on jack stands for more than 24 hours.
(Any Utah / SLC members lurking around the form? PM your shop of choice if you are.)
 
Sounds like my 67 273 2bbl.

With vacuum advance on it misfires at around that same rpm. I'm at 5 before.

Spec is 5 after (CAP)

I checked the dwell and with the vac on it goes down way down and starts to misfire. Without the vac the dwell stays fixed and no misfire. Could be too much total advance? Could be dwell changing too much?

You dusted off an old memory with your comments above about variations in dwell.
That is the the 'point cam' wearing out and causing said issues. I've had to change several of those way back in high school .
Today's points are not what they used be either...
Also too, factory tuner is almost never optimum.
 
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