355 sbc bogs when at idle and hot

[wrxand280z]

I'm having some issues with my 355 chevy. It runs and idle fine until it gets hot and sparatically it will start idling really rough and will even cut off. After a minute or two it stops running rough and idles fine. I thought it was a coil going bad so I replaced the rotor, cap and coil but it still does it. It seems like it its either loosing fire or something in the fuel. I'm also getting 13-14 mpg and running 87 octane. I've just had the timing set. Any thoughts?

[BRAAP]

I'm assuming carbonated, Holley, Edelborck, Carter, etc?

 

When it is running rough at idle, have you tried to readjust the idle mixture to clear it up? If so and it does not clear up, then Ignition Module comes to mind, especially being heat related. Are you running HEI? If HEI, don't skimp on the ignition module, get a quality one and be sure to install it per the instructions. Most use a grease/lube for heat transfer to the dizzy base which helps tremendously in the longevity of the ignition module.

 

Fuel wise, intermittent issues such as this are typical of particles floating around in the float bowls not allowing the float needle to seat or partially clogging the jets.

 

Hope that helps,

 

Paul

[wrxand280z]

Braap,

Thanks for the response. I have not tried to adjust the idle as I'm usally in a drive thru line when it happens. It takes a while of sitting for it to do it. Do you recommend a brand of ignition module or would Napa brand do?

It is an edlebrock 750 with HEI.

[BRAAP]

I’m sure many of the aftermarket performance modules would be just fine from MSD, Pertronix, ACCEL, D.U.I., Mallory, etc.

 

This HEI article refers to matching the module to the coil;

http://www.chevyhiperformance.com/techarticles/67498_hei_coils_modules/index.html

 

This article discusses improving the HEI. (Another great HEI article...)

http://www.automedia.com/HEI_Ignition_Upgrade/pht20021001he/1

 

 

Courtesy of ChevyHighPerformance.

 

 

All performance modules come with a high-heat-transfer white grease that conducts heat away from the module to help keep it cool.

Heat is the biggest enemy of the HEI module.

 

 

 

Hope that helps..

[dr_hunt]

That is di-electric grease which is non electric conducting grease. You can't use regular white grease. You can buy that at Napa if you happen to need some more when using an old module. Be sure to use pleanty rather than skimp on that.

[wrxand280z]

I'm running a T56 in my 78 280. Shouldn't I be getting better gas mileage? I'm not really stomping on it and the tire pressure is up. Would a bad ignition module have something to do with this too?

[Pyro]

i bet your carb is vapor locking (fuel boiling in the bowls). Edelbrock says their aluminum carbs cool the fuel quicker after shut down but fail to mention that they also heat the fuel up quicker when running. hahahaha.

 

If you have hood clearance for a 1 inch thick carb insulator it will help. Otherwise buy a Holley or q-jet, these carbs don't transfer as much heat to the fuel bowls. You could also close off the manifold exhaust crossover under the carb.

 

I had 2 edelbrock carbs and threw them both in the trash. Edelbrock makes good intakes but bad carbs.