Incorrect Timing Adjustment causing heat issues?

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jau126

'65 Dart GT 273 904
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Jun 7, 2020
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Salt Lake City, UT
I recently installed a new 4 barrel and decided to take it to a shop that has more equipment to dial in the fuel trims so I am not running as fat as a pig up at altitude. The shop tech in the process adjusted the timing (I am not sure what the pass timing is now as I just picked it back up and will check in to it tomorrow) and now it seems to be getting warmer than usual.
I do not think this is carb or cooling problem directly as 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.
Am I wrong to think that the timing effect heat into the block? And should I take it back to them to make them correct the issue?
From what I understand they set the fuel to be at 4% CO so around 13.0 AFR but of course the guy who seems to run the place didn’t have any more info.
(273 with 904 no fan shroud if that make a difference here)
 
Retarded timing can cause a temp increase. You’d have to be off quite a bit to see 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?
 
It's possible they screwed it up.
You are correct that retarded timing can cause the engine to run hotter. It was done on purpose (at idle only) on CAP packages.
It will also lose umph or throttle resposne if the whole curve is retarded.
You are correct standard timing for 273 4 bbl should be around 10 * BTDC somewhere around 550-600 rpm. The rpm it is set at is VERY important.
Also the distributor you are using will make a difference on the advance above idle. So tell us what you have,
 
It's possible they screwed it up.
You are correct that retarded timing can cause the engine to run hotter. It was done on purpose (at idle only) on CAP packages.
It will also lose umph or throttle resposne if the whole curve is retarded.
You are correct standard timing for 273 4 bbl should be around 10 * BTDC somewhere around 550-600 rpm. The rpm it is set at is VERY important.
Also the distributor you are using will make a difference on the advance above idle. So tell us what you have,
Absolutely. You may have been getting some pinging because of the advance but the distributor may be advancing too fast or too far. You will need to read up on that and check it out with a timing light.
 
Is it possible that I need a new cap, rotor and condenser if the accidental left the key in the run position while off?
Forgot to answer this.
Cap and rotor would not be impacted.
If the points were closed its possible they got some surface damage. Look and see - clean 'em up if needed. If left closed for a real long time, then possibly coil got cooked or even a connection somewhere along the current path. If and possibly, not neccessarily.
 
My understanding is the hottest temperatures are generated around the rich side of stoich. (I'll have to dig that info out to verify)
A very lean condition will result in loss of power. That's how it normally shows up when driving. When its happened to me, the engine has revved and then died. Sometimes it will catch again, especially if when the throttle is closed down somewhat.
At idle, a lean condition will show up when load is applied. With automatics, that is as simple as placing it in gear. The little additional load from the transmission pump will cause the rpms to noticably drop.
 
I've honestly worked on a few that we're pretty rich and I never noticed that they we're warmer when leaned out. That could be coincidence, but it has been my understanding the leaner conditions can cause the temps to be warmer. I could honestly see either way, I'm just not sure.
 
A leaner mixture provides less fuel to cool the cylinder
But I am not sure that running @13.0 afr would cause the heat. There should still be extra fuel present.
 
It is true that under certain conditions running an excess of fuel can help reduce hot spots and provide some cooling.
Under the same compression and other conditions, different fuel air mixtures will generate increasing burn termperatures as you go from rich toward stoich, but then leaner than stoich burn termperatures decrease.

Some discussion of that at the begining of this archived thread.
 
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they apparently adjusted it because it was “misfiring” at around 2500 rpm
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?
 
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?
I'd say dial a little out of the vacuum advance; either by increasing the spring load (takes more vacuum to move it) or limiting how much it can add.
With a CAP distributor, it was designed to advance so quickly that well before 2500 rpm timing would be essentially the same as a non-CAP engine.
So with 10* more initial than spec, timing at 2500 is 10* more than spec. There of course was some latitude (esp on non-CAP) to adjust initial a couple degrees for local conditions and fuel. But 10* apparently is a little too much.

Lemme see if I have plotted the 67 Plymouth 273 2 bbl timing curves.
 
As some 64,65,66 Dart owners got into this (@slantsixdan) he brought up the point that although I have a closed crank case system ventilation system that was not truly cap and should not have a cap timing curve in it as that was not available in 65 even in California.
Edit: I will add though when I purchased the car it was set a 5 ATDC with the vacuum advance connected for base timing. I initially adjusted that to 5 ATDC with vacuum advance disconnected and made a significant difference with cooling. It also seemed to jump to a reasonable advance on the smallest amount of throttle opening. But I am nut sure if that is a function of the vacuum advance or if that is a mysterious CAP timing curve where it shouldn’t be
 
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The biggest diagnostic issue on timing for me is one man two arms and the dumb 65 timing mark on the passenger side with throttle on drivers
 
Lemme see if I have plotted the 67 Plymouth 273 2 bbl timing curves.
@Dana67Dart

Here you go. Timing range for 1967 273 2bbl with AT, and 2 bbl CAP with initial set at the recommended.
upload_2020-9-24_21-22-1.png


And this illustrates how the mechanical timing shifts when the initial for a CAP distributor is changed to 5* BTC
upload_2020-9-24_21-31-7.png


Shop manual shows the same vacuum timing specs for CAP and non-CAP
At 13.5" of Hg and above it should add 21 to 27 degrees of advance.
 
Well unless it was retrofitted for some reason I don’t think it should have one. It also doesn’t have the CAP valve
 
There should be a tag on the dist see if you can get a number.

Also if you pull the vac advance hose off does the misfire go away?

I'm not saying that your misfire is like mine. It was just interesting to here someone else say the same thing.

Also check the dwell at idle vs at 2500 wondering if it is super low like mine goes
 
I initially adjusted that to 5 ATDC with vacuum advance disconnected and made a significant difference with cooling. It also seemed to jump to a reasonable advance on the smallest amount of throttle opening. But I am nut sure if that is a function of the vacuum advance

Three things need addressed here:

1. Why are you setting your base ignition timing to anything ATDC? Spec timing for a '65 273-2bbl is 5° Before TDC (manual transmission), 10° Before TDC (automatic transmission), without the vacuum advance hooked up. Retarded timing (after TDC) causes hot running by a very simple chain of events: spark occurs late, so fuel/air mix still burning when exhaust valve opens, so cylinder head heats up extra-hot, which heats up the coolant…and exhaust manifolds and headpipes heat up extra-hot, too, which heats up the underhood air.

2. It sounds like you have significant vacuum going to the vacuum advance at idle. You shouldn't. Make sure the vacuum advance is hooked to the correct port on the carburetor, and if it is supplying significant vacuum at idle, either that's another problem being caused by the incorrect base ignition timing (retarded timing causes slow idle, so you crank the throttle plates open with the idle speed screw, which uncovers the spark advance port, sending vacuum to the distributor) or there's a problem with the carb (throttle plates not closing correctly). Find and fix this problem.

3. Why are you so fixated on a Clean Air Package your car does not have? :·)
 
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There should be a tag on the dist see if you can get a number.

Also if you pull the vac advance hose off does the misfire go away?

I'm not saying that your misfire is like mine. It was just interesting to here someone else say the same thing.

Also check the dwell at idle vs at 2500 wondering if it is super low like mine goes
I will look in to that tomorrow.
 
Three things need addressed here:

1. Why are you setting your base ignition timing to anything ATDC? Spec timing for a '65 273-2bbl is 5° Before TDC (manual transmission), 10° Before TDC (automatic transmission), without the vacuum advance hooked up. Retarded timing (after TDC) causes hot running by a very simple chain of events: spark occurs late, so fuel/air mix still burning when exhaust valve opens, so cylinder head heats up extra-hot, which heats up the coolant…and exhaust manifolds and headpipes heat up extra-hot, too, which heats up the underhood air.

2. It sounds like you have significant vacuum going to the vacuum advance at idle. You shouldn't. Make sure the vacuum advance is hooked to the correct port on the carburetor, and if it is supplying significant vacuum at idle, either that's another problem being caused by the incorrect base ignition timing (retarded timing causes slow idle, so you crank the throttle plates open with the idle speed screw, which uncovers the spark advance port, sending vacuum to the distributor) or there's a problem with the carb (throttle plates not closing correctly). Find and fix this problem.

3. Why are you so fixated on a Clean Air Package your car does not have?
I am not fixated on it. All I am saying is that the car when I purchased it, was firing after TDC at idle. At that point in time I believed it needed to be there and was correct. I know that it is not and I moved it 10 degrees BTDC.
Vacuum canister is hooked up to ported not manifold and when I set it before taking it to the shop that did the work it seemed fine. (I could remove and plug the port and not notice any difference in timing at idle.)
 
Here is a question that no one has answered:
Should I take it back to them and show them what they messed up and make them fix it? I am worried it turns out to be a fueling issue they will say I messed with it and I will have to pay them all over again.
 
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