Opinions on preliminary tune welcome----

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DesertRat

DesertRat

Leading edge boomer
Joined
Jan 22, 2005
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Location
Moses Lake, Washington
The build: 1967 273, Stock heads, 10.5 Egge pistons .040 over, Lunati matched cam, hydraulic lifters & springs, LD4B intake with Holley 4160. Duration @ .050-IN 213 EX 220 lift IN .454 EX .475, LSA 112. About 2 hours total run time, 150# compression on last check.
The tune: Stock distributor with Pertronix conversion, coil & wires, distributor recurved to 34 total from 12 initial all in at 2500. Hot in gear, idle at 700 rpm with 8" of vacuum. In neutral idle goes to 1000 rpm, forgot to check vacuum.
I have not checked jets size but the factory AFB wanted .089 mains and .073 secondary's.
Just wondering about the vacuum, seems a little low and I will be changing power valve based on hot idle vacuum.
Insight welcome as always-------------Cheers---------DR:)
 
leave a 6.5 power valve in it.

Below is one of the things I would do.

SETTING TIMING CURVE

Before you start driving it normally, I would set the timing curve so it is optimum for your particular setup . Below is just one way to do that . In general, the goal is to run as much timing as possible without it pinging under heavy load.

The more timing you have, the more vacuum it will have until the timing reaches its optimum level.

The more vacuum it has, the smother it will idle and the more you can close the butterflies.

If the butterflies are too far open, you will be into the transition circuit of the carb which can cause idle problems . One of the indicators that the butterflies are too far open at idle is when the carb has vacuum at the ported vacuum port.

1. Disconnect and plug the vacuum hoses to the dist if you have any and leave them plugged permanently or until further notice.

2. Reduce idle as much as possible then start your timing at 10 degrees BTDC.

3. With the engine warm and idling, advance the timing 4 degrees . Listen for a slight but noticeable increase in rpm and irregular/rough running . Also use a tach or vacuum gauge if you have one.

4. If the rpm increases and it still runs smoothly, reset the idle speed then increase the timing 2 more degrees and check for the same things.

5. Retard timing back to 10 degrees btdc.

6. Reset the idle speed.

7. Increase the rpm to around 2000 then advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

8. If the rpm increases and it still runs smoothly, reset the engine speed to 2000 rpm then increase the timing 2 more degrees and check for the same things.

POST RESULTS


TEST DRIVING

After setting the timing curve you can do the following test to see if you have too much advance.

Get the engine up to operating temp.

Drive at around 20 mph in second gear for a few seconds then floor the gas pedal as fast as you can until you reach around 30 mph and listen for even the faintest pinging sound coming from the engine . If it pings, you have too much timing for the octane gas you are using . You can either reduce the timing some or use a higher octane . The highest timing level you can run without it pinging and/or running erratic will SAFELY provide the most power.

It may ping in hot weather even if it does not in cold weather . If you find this to be the case, the easiest thing to do is reduce the timing until it stops or try higher octane gas . If it still pings with the highest octane gas, you can reduce the timing then.
 
Everything I have done has been with tach and vacuum gauge on manifold vacuum. This combo really likes 15-16 initial advance a lot better than 10 or 12 initial. Runs a lot better and has a lot more manifold vacuum. Not monitoring ported vacuum at all. CB-should I go back to 16 initial and leave it there and tune from there?
 
DesertRat said:
Everything I have done has been with tach and vacuum gauge on manifold vacuum. This combo really likes 15-16 initial advance a lot better than 10 or 12 initial. Runs a lot better and has a lot more manifold vacuum. Not monitoring ported vacuum at all. CB-should I go back to 16 initial and leave it there and tune from there?
Click to expand...

You should do the timing test I posted at 2000 rpm now that you have established the best timing for idle . After you post the results, we will have a good idea what your total timing should be . You may need to change the springs in your distributor and you may not.
 
OK, I will test it, I have already put a limit plate in the distributor and am running one medium spring. No vacuum advance has ever been connected yet. I know it will increase vacuum and RPM when I advance it to 16+ advance. I don't think I was into the transfer tubes on my timing this morning but I can check the ported vacuum before I start to check it. Thanks for the help guys!
 
DesertRat said:
OK, I will test it, I have already put a limit plate in the distributor and am running one medium spring. No vacuum advance has ever been connected yet. I know it will increase vacuum and RPM when I advance it to 16+ advance. I don't think I was into the transfer tubes on my timing this morning but I can check the ported vacuum before I start to check it. Thanks for the help guys!
Click to expand...

It sounds like you already have a very good idea how to time it and check to see if you are into the transfer slots so this will be a piece of cake for you.

I f you have a holley, i set the gas level so it is just below the inspection holes at idle or immediately after turning the engine off . If it has clear sight windows, I set it so the gas is 1/4 up the window at idle.
 
with that low vacuum @ idle.... a 6.5 PV is to "big "...go for a 4.5 PV and you will save a lot of gas...
Greetings Juergen
 
I had that same cam in a worn-out stock 318 and it pulled WAYY more vacuum at idle; even though yours is a smaller 273 the fact that it's healthy and has good compression should make it idle just as well. I was getting almost 12" of vacuum in gear and my initial was no more than 10-12 degrees... something is up IMO
 
Went through the drill again this morning. Reset initial to 17 degrees and set idle at 700 rpm hot in gear and reset the idle mixture screws. Finished up with 11" vacuum hot in gear at 700 rpm and 16" hot in neutral at 900 rpm. At 2000 rpm it is pulling 19" of vacuum and sounds like it wants to be let loose! Next step, check jet size against the FSM callout for the AFB and if a change take place, I will leave the initial alone (it really likes it there) and readjust the idle circuit. Plugs have been running black and I suspect it is a bit rich but the float level is correct so I have to sort that out and probably change the power valve to a 5.5 or 6.5. I know the valve adjustment is correct and the timing marks and TDC are all correct. Thinking about putting it on the ground and test driving it this weekend. (no front fenders or front or rear glass:) Chime in if you feel like it, I think the indicators are good. I have decided to fabricate my own fan shroud as the available ones seem flakey to me.
Cheers to all--------------DR--------------:)
 
ok, if the porcelain is black, you need to go down 2 sizes on the front main jets and try that.
 
DesertRat said:
Went through the drill again this morning. Reset initial to 17 degrees and set idle at 700 rpm hot in gear and reset the idle mixture screws. Finished up with 11" vacuum hot in gear at 700 rpm and 16" hot in neutral at 900 rpm. At 2000 rpm it is pulling 19" of vacuum and sounds like it wants to be let loose! Next step, check jet size against the FSM callout for the AFB and if a change take place, I will leave the initial alone (it really likes it there) and readjust the idle circuit. Plugs have been running black and I suspect it is a bit rich but the float level is correct so I have to sort that out and probably change the power valve to a 5.5 or 6.5. I know the valve adjustment is correct and the timing marks and TDC are all correct. Thinking about putting it on the ground and test driving it this weekend. (no front fenders or front or rear glass:) Chime in if you feel like it, I think the indicators are good. I have decided to fabricate my own fan shroud as the available ones seem flakey to me.
Cheers to all--------------DR--------------:)
Click to expand...

Now THAT's more like it! Take that thing for a spin, if your local cops aren't total jerks they should understand it's a work-in-progress lol.

Also I agree with barnett468 try dropping the primary jet size down a couple sizes and see if it cleans up the spark plugs. It will need to be driven for a while for all that carbon to burn off though so don't expect them to miraculously clear up right after the jet change.
 
The FSM calls for 89's in the primary's of the stock 600 AFB. I will blow the Holley apart tonight and see what I have in the primary's and secondary's. I picked up a 6.5 power valve for it as I don't know for sure what is in the thing off the shelf either jet-wise or PV wise. I know I am getting closer though. Anyone have a idea for jet sizes for a Hi-Po 273 out .040 using a Holley 4160 vacuum secondary carburetor? I have the spring kit for tuning the secondary's when I can actually put it under load. I need a chassis dyno in my garage-----:)
Hot in the desert heat------DR------:)
 
DesertRat said:
The FSM calls for 89's in the primary's of the stock 600 AFB. I will blow the Holley apart tonight and see what I have in the primary's and secondary's. I picked up a 6.5 power valve for it as I don't know for sure what is in the thing off the shelf either jet-wise or PV wise. I know I am getting closer though. Anyone have a idea for jet sizes for a Hi-Po 273 out .040 using a Holley 4160 vacuum secondary carburetor? I have the spring kit for tuning the secondary's when I can actually put it under load. I need a chassis dyno in my garage-----:)
Hot in the desert heat------DR------:)
Click to expand...

Hang on a sec, if all the tuning you've been doing so far has been with the engine running under no load then I'd just wait until you can test-drive the car before you start changing jets. Definitely good idea to know what you have in there but until the engine is seeing realistic load and driving conditions you won't be able to tune anything except the idle mixture correctly...
 
DesertRat said:
The FSM calls for 89's in the primary's of the stock 600 AFB. I will blow the Holley apart tonight and see what I have in the primary's and secondary's. I picked up a 6.5 power valve for it as I don't know for sure what is in the thing off the shelf either jet-wise or PV wise. I know I am getting closer though. Anyone have a idea for jet sizes for a Hi-Po 273 out .040 using a Holley 4160 vacuum secondary carburetor? I have the spring kit for tuning the secondary's when I can actually put it under load. I need a chassis dyno in my garage-----:)
Hot in the desert heat------DR------:)
Click to expand...

barnett468 said:
ok, if the porcelain is black, you need to go down 2 sizes on the front main jets and try that.
Click to expand...

Also, clean the plugs with a brush and carb cleaner the best you can first.

Also, I usually only have a 4 jet size different from the front to the back with the back being bigger.
 
barnett468 said:
Also, clean the plugs with a brush and carb cleaner the best you can first.

Also, I usually only have a 4 jet size different from the front to the back with the back being bigger.
Click to expand...

Keeping in mind that I can test drive the car maybe to 30 mph for 30 minutes in its current condition I don't know what that will show me. You mention 4 jet size differential between primaries and secondary's, the larger in the secondary's, is that for a Holley? As I stated, The FSM calls for 89's in the mains and 73's in the secondary's but that is a Carter AFB, different engineering characteristics I guess. I need a baseline for a Holley.
BTW, thanks to all for the advice, I appreciate it!
 
At 30 mph you may not even be on the main jet.

Don't use the carter jetting for any kind of reference on a holley.
 
crackedback said:
At 30 mph you may not even be on the main jet.

Don't use the carter jetting for any kind of reference on a holley.
Click to expand...

Thanks, I won't reference the carter jetting. I have 3:73.1 SG gears. I think in low I can get on the main jets:)
I MAY put it on the ground Sunday and take it for a spin. If I do I will post photos on my build thread. Quite a few
things to sort before I take it off the stands. I really need a nice fan shroud and may elect to build and install that
before I test drive it. I wish you guys could hear it run, sounds like a caged dinosaur rumbling:)
 
Find the LIST # on your holley and start with the factory jetting.

30 mph in low is not a normal driving condition and little if nothing you see regarding plugs/jetting should be considred.
 
crackedback said:
Find the LIST # on your holley and start with the factory jetting.

30 mph in low is not a normal driving condition and little if nothing you see regarding plugs/jetting should be considered.
Click to expand...

Ok, thanks. I just made arrangements to access a sheet metal brake so I will be building my fan shroud this weekend.
No more tuning or driving for me until I get things sorted. The car is tuned nicely for the state of the build, I will finish up the
rest of the engine bay and get the front end of the car on before I take it out.
Cheers to all and happy TGIF eve-----------------DR------------:)
 
Hey wait, I installed a o2 wide band sensor as part of the build, why don't I tune the carburetor with my new innovate wide band sensor. (Head slap-silly me)
 
DesertRat said:
Hey wait, I installed a o2 wide band sensor as part of the build, why don't I tune the carburetor with my new innovate wide band sensor. (Head slap-silly me)
Click to expand...

because you cant do it using the sensor only . you need to take plug readings also and seat of the pants performance info as well . doesnt matter if the meter says your afr is "ideal" if the spark plugs are black or lilly white.
 
150# seems a little low. Where did you install the cam?
 
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