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Old 01-24-2021, 04:09 PM   #1
srg
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Default Runs great until it heats up

1937 with a 59AB engine, offenhauser manifold, sharp heads, denton headers, two stomberg 97 carbs. Has a mallory electronic distributor with the corresponding coil. It ran great before. Now it runs great until it gets hot and starts to miss and evolves into stalling with the foot off the gas. It STARTS immediately every time after it stalls, but resumes running with mega missing, until it stalls again. Any ideas? Ignition? But it starts every time after stalling, but misses bad. It recovers while missing if I pump the gas pedal like crazy but drops back into mega missing. Carbs? It starts and runs great until I am at temperature for a while (160-180). Coil? Resistor?
There is a strange sound coming out of the engine when this condition presents, like one side of the engine isn't firing the fuel, kind of a gurgling.

Brain stormers needed. Thanks guys.
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Old 01-24-2021, 04:18 PM   #2
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Default Re: Runs great until it heats up

Try another coil. In a '36 coupe I had a few yrs ago similar to yours (Sharp Heads,Mallory ign 2 97's)except for a Potvin super cam .When coil got hot ,car stalled and died.Let it cool down and it would start right up and then 3 miles later died.I replaced the coil and that cured it.
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Old 01-24-2021, 04:44 PM   #3
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Default Re: Runs great until it heats up

Coil .......
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Old 01-24-2021, 04:45 PM   #4
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Default Re: Runs great until it heats up

Mine was also coil................
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Old 01-24-2021, 06:31 PM   #5
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Default Re: Runs great until it heats up

That's the most likely suspect, but it might also be the condenser. They can fail when hot as well.
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Old 01-24-2021, 06:46 PM   #6
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Default Re: Runs great until it heats up

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Check the primary resistance on the coil. Mallory is notorious for providing the wrong coil. With a 12v system, you'll want a total of about 3.5 ohms resistance.
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Old 01-25-2021, 12:06 AM   #7
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Default Re: Runs great until it heats up

But guys, what about this symptom from the original post:
"It recovers while missing if I pump the gas pedal like crazy"
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Old 01-25-2021, 12:19 AM   #8
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Default Re: Runs great until it heats up

Agree with Jay. Maybe fuel related... Could be anything really. But maybe the ignition is recovering just enough to run poorly.


If it runs well every time its started from a normal cold state, and it only acts up under warm (160-180) conditions. I don't think its a vapor issue.


Clean plugs, run it till it fails. Check plugs.


***Normally I would say when its stalling to pull the choke slowly and if it runs better, then it's a lean condition. But you have a dual setup. If the primary has a choke that you can run manually. try that. Just a thought.

Last edited by Tinker; 01-25-2021 at 12:45 AM.
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Old 01-25-2021, 12:47 AM   #9
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Default Re: Runs great until it heats up

Thanks Deuce. Mine starts right back up, even while hot, but resumes missing like crazy. Start it up while cold, no problem.
Jay: When I mentioned "it recovers" when pumping the gas, it would be more accurate to say I can coax it down the road a bit doing that, but the missing with resulting noises from the engine catch up with me and it stops running. I roll to a stop, push the start button, it starts right up but misses badly, then stops again. I've coaxed it back to my garage by pumping the pedal furiously. I appreciate all you're guys help. I'll check that coil. I put my hand on the coil when I got it back yesterday and that sucker was hot. It's mounted right next to the manifold above the left head in the front of the engine.
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Old 01-25-2021, 12:52 AM   #10
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Default Re: Runs great until it heats up

Condenser or coil... But I'd mention valves sticking. My truck that's rebuilt does this every spring after sitting. It idles just fine till I put load on it. It bucks underload. I do a mmo carb dump every spring and it clears it up. I know the idea of the mmo thing is a bit lame. But it works.
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Old 01-25-2021, 01:08 AM   #11
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Default Re: Runs great until it heats up

Vacuum leak on the intake manifold and its running lean (too much air) thats why it picks up when you pump the accelerator pump and it gets more fuel to even up the mixture. Connect a vacuum gauge to the intake manifold for a test. Regards Kevin.
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Old 01-25-2021, 02:49 AM   #12
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Default Re: Runs great until it heats up

Quote:
Originally Posted by koates View Post
Vacuum leak on the intake manifold and its running lean (too much air) thats why it picks up when you pump the accelerator pump and it gets more fuel to even up the mixture. Connect a vacuum gauge to the intake manifold for a test. Regards Kevin.

adding a little choke when it's running underload will also decrease air flow.
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Old 01-25-2021, 03:04 AM   #13
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Default Re: Runs great until it heats up

As Koates says plus a vacuum leak will cause it to idle rough.
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Old 01-25-2021, 06:07 PM   #14
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Default Re: Runs great until it heats up

Tinker: What's an MMO carb dump?
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Old 01-26-2021, 02:02 AM   #15
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Default Re: Runs great until it heats up

I think its Mystery Marvel Oil and maybe he pours it in the air horn.Never heard of that remedy.Sounds like your setup is pretty fresh so the shouldn't be necessary.
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Old 01-26-2021, 03:10 AM   #16
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Default Re: Runs great until it heats up

start with coil then condenser and also check that the dissy advance is not jammed or worse broken springs
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Old 01-26-2021, 07:57 PM   #17
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Default Re: Runs great until it heats up

Many posts w same over the years, mot of the time Coil or condenser bad. Didn’t quite understand when it occurs? If in neutral does it happen or just under load?
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Old 01-27-2021, 12:12 AM   #18
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Default Re: Runs great until it heats up

Quote:
Originally Posted by deuce lover View Post
I think its Mystery Marvel Oil and maybe he pours it in the air horn.Never heard of that remedy.Sounds like your setup is pretty fresh so the shouldn't be necessary.

Lead was used for L head motor upper cylinder lucubration. Guess it's a thing, as they sell lead additive now. Which I would never buy.

On a new rebuilt motor like mine the tolerances are very tight and every amount of lubrication in the valves/guides help on a L head motor.

Just pour mmo down the carb at idle till it smokes out. Then drive the crap out of it. Rinse, repeat.

Maybe I'm wrong, but sticky valves do happen. As I mentioned it could be a lot of things. Like the coil and condenser.... maybe the Mallory is being weird? Don't know, I run points.

Last edited by Tinker; 01-27-2021 at 01:33 AM.
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Old 01-27-2021, 08:30 PM   #19
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Default Re: Runs great until it heats up

Anthony: Happens under load and idling.
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Old 01-27-2021, 08:38 PM   #20
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Default Re: Runs great until it heats up

Thank you guys. This is my attack plan: 1. Take all connectors off of coil and resister and clean them. Test. 2. Check intake manifold. Test 3. get new resistor. Test. 4. Get new coil. Test. The resistor (OEM) under the dash is disconnected. I'll carefully inspect spark plug wires and coil resistor wiring. Here's something that happened I haven't thought about; the dudes at the body shop welded on the car without disconnecting the battery. I believe that's a very bad idea.
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