Rough running 440 when engine warm and sits a while

[W4ATL]

I have been working on a nagging issue with my 68 Charger with a 440. It runs great when started cold and driving around. If I park it for about 5-30 minutes and then start back up it idles a bit rough and stumbles on hard acceleration. I put a new coil on it and fiddled with the timing and it seemed to help but it still happens, although not as bad as before. The coil I used was a MSD Blaster 2 Ignition Coils 8200 from Summit to replace the old NAPA one. I also tried to thermally insulate the coil with some extra gasket material and it improved somewhat but still stumbles when hot after parking. If it is a coil heating issue can someone recommend a good one? I'd rather not move it since I don't have room on the passenger side of the engine bay and I would like it to look stock.

[alfaitalia]

Sounds more like a fuelling issue to me... Vapourising causing starvation perhaps.

[TommyGun]

Choke sticking on?  What kind of carb?

[W4ATL]

Choke sticking on?  What kind of carb?

AVS. I'll check the choke.

[W4ATL]

Choke sticking on?  What kind of carb?

AVS. I'll check the choke.

Engine was stumbling after it warmed up on a warm day. I checked the choke and it was wide open. I'm still leaning toward a hot coil.

[Bad B-rad]

I have to agree that sounds like a fuel issue.
What intake are you using?
(thoughts are aluminum intake with heat cross over,vs the cast iron one,may need to insulate carb with better gasket/ spacer, just thoughts)
You could always move the coil to the fender, with zip ties and insulate it , just to test your "hot coil" theory. And if the issue goes way then you can handle the new coil and mounting it in stock location issue, and if you move it to fender and insulate it and issue continues then you can put it back and move on.
But I think fuel is were you need to look., just my 

[c00nhunterjoe]

Sounds like heat soak. IntKe crossover blocked and insulated carb spacer from coolcarb technologies. Will look stock still.

[W4ATL]

 I installed a Edelbrock 9266 heat insulator carb gasket which has drastically improved performance. I had some slight stumbling on a 90 degree day with the A/C on but nothing like before, so I am starting to think we are on to something with the hot carb.

But now I have a new problem. The engine "whistles" from about 1500-2000 RPM when under load. I can vary the tone of the whistle with the accelerator. If I gun it so the RPM is over 2K it goes away. Also goes away under light load. I can't make it happen under no load in the garage. The whistle is still there with the air cleaner off. All of the vacuum hoses are back in place and appear to be in good condition.

[Bronzedodge]

When I had that whistle problem there was a carb to intake leak with my Holley.   

[W4ATL]

When I had that whistle problem there was a carb to intake leak with my Holley.   

I agree. The instructions said gaskets were not required since this insulator is a gasket but I'm having doubts.

[69wannabe]

You really need to do the blocked crossover intake gasket if you have not done this yet. It will make a difference but with the facotry AVS and intake heated choke I don't know how good that may work. This ethanol fuel we are having to deal with has a lower boiling point than the old gas we were used to 10 years ago and causes heat soak to be alot worse than it used to be. Had my fuel line ran up behind the alternator like the factory had it and moved it over to the firewall and used thermo wrap sleeving above the valve cover and header and done the cool carb technology's spacer kit and my heat soak is down to a minimum on my car at this point. The AVS is aluminum and get's hot very quick like an edelbrock carb. This is a problem we are all dealing with and there are several thing's to do to help keep it from being so bad in these hot summer month's.

[alfaitalia]

"This ethanol fuel we are having to deal with has a lower boiling point than the old gas we were used to 10 years ago and causes heat soak to be alot worse than it used to be".


Not really. Ethanol is a pure substance that has a boiling point of about 172.4F. Gasoline is a compound of lots of chemical elements which boil off between 95 and 375F. So adding ethanol at the typical 15% mix will not affect the overall boiling point of the fuel to the level you could measure/feel it in your car. Its barely measurable in the lab!

[lukedukem]

http://www.dodgecharger.com/forum/index.php/topic,52284.0.html

Luke

[72Charger72]

My 440 used to do the same thing...vapor locking.....hot carb....get that thing as far up off the manifold as possible. Add some heat dispersion plates...

[69wannabe]

"This ethanol fuel we are having to deal with has a lower boiling point than the old gas we were used to 10 years ago and causes heat soak to be alot worse than it used to be".


Not really. Ethanol is a pure substance that has a boiling point of about 172.4F. Gasoline is a compound of lots of chemical elements which boil off between 95 and 375F. So adding ethanol at the typical 15% mix will not affect the overall boiling point of the fuel to the level you could measure/feel it in your car. Its barely measurable in the lab!

Why are we having these heat soak issues now and not before the ethanol mix fuel showed up. In 2007 I had my carb bolted directly to the intake with a thin gasket and had no fuel boiling issues that I remember. In 2010 tore the car down and made some changes, got it back up and running in 2012 and had heat soak issues something terrible til I did all the recommended block off's and spacers to get it down to a minimum. So you tell me what changed?? Nothing else changed in the car since it was down for body repairs and not mechanical repairs and why all the sudden is everybody having to deal with this fuel boiling issue that didn't really seem to be an issue before ethanol came along? It's a fuel issue either way lab or no lab.....

[W4ATL]

Installed the Felpro 1215, Edelbrock carb spacer and while I was at it a new Edelbrock 750 CFM 1411 carburetor with the electronic choke. The rough running when warm is gone so it was a vapor lock issue with the carb. The new carb is fantastic. Throttle response has never been better and I am pleased with the results. For those that want to install the Felpro 1215 I did have issues with the intake fitting with the this thicker gasket. The bolts did not want to line up due to the additional thickness. Making the holes on the intake slightly bigger allowed me to get all the bolts started and the intake installed. I'm not sure why others didn't mention this problem.

I do have a slight whistle problem but it is not nearly as bad as when I put the spacer in with the old carb and no block of the heat crossover. It only whistles when very warm at a certain RPM. Otherwise it is quiet.

[c00nhunterjoe]

Installed the Felpro 1215, Edelbrock carb spacer and while I was at it a new Edelbrock 750 CFM 1411 carburetor with the electronic choke. The rough running when warm is gone so it was a vapor lock issue with the carb. The new carb is fantastic. Throttle response has never been better and I am pleased with the results. For those that want to install the Felpro 1215 I did have issues with the intake fitting with the this thicker gasket. The bolts did not want to line up due to the additional thickness. Making the holes on the intake slightly bigger allowed me to get all the bolts started and the intake installed. I'm not sure why others didn't mention this problem.

I do have a slight whistle problem but it is not nearly as bad as when I put the spacer in with the old carb and no block of the heat crossover. It only whistles when very warm at a certain RPM. Otherwise it is quiet.

The valley pan with and without the heat crossover are the exact same thickness. The paper gaskets included in both kits are not used on stock deck engines.

[69wannabe]

Glad you got it going and got the fuel issue under control!!!!