Running poorly after warm and restart? (1 Viewer)

[85roktoy]

After driving 10-15 mins and shut her down she’s running really rough once I restart. RPM’s fluctuating and sluggish (almost hesitating) during acceleration up through the gears. Once I get going 10 or so minutes she smooths out again. No more surging or rough idling. Shut the motor off and wait 10-15 mins and same thing happens every time. Runs really rough until she gets going again. Where do I start? Everything is original no factory carb fan. I’m thinking it’s carb related but not sure

 

[cbmontgo]

Sounds like a bit of vapor lock to me. My 40s do the same thing when temperatures warm up outside. Try non-ethanol gas and see if it helps a little.

 

[85roktoy]

Sounds like a bit of vapor lock to me. My 40s do the same thing when temperatures warm up outside. Try non-ethanol gas and see if it helps a little.

Was thinking the same thing but reading that would cause it to not start at all. It does take longer to start so hummm…

 

[Pighead]

Sometimes mine likes a little choke for a minute even when it's warm

 

[cbmontgo]

Was thinking the same thing but reading that would cause it to not start at all. It does take longer to start so hummm…

Depends on temperature, type of gas, whether you are desmogged, etc. My original ‘76 vapor locks much differently than my partially desmogged ’77.

If your issue only happens in warmer weather, then I’d bet money on it. Gotta either get a pusher fuel pump, go EFI, or learn to live with it.

 

[85roktoy]

It happens in the winter too but this is FL so not much of a winter. Going sniper soon so hopefully that will help or cure it…

 

[JDNs78FJ40]

I don’t know anything about anything but I’ve been messing with my timing lately and now that I’ve dialed that in it purrs like a kitten… I mean tractor. I do have the sniper though.

 

[mrboatman]

Sounds like when you shut it down it is boiling the fuel out of carb fuel bowl and flooding. Then takes a while to start and clear it out.

 

[Malleus]

It was a habit of my grandfather (who grew up driving in the late 30s) to put the pedal to the floor when he turned off the ignition, both to
"raise the oil pressure for the next time the engine stated" and to prevent the carburetor from starving on startup. Even after he bought cars and trucks with EFI, he contiunued to do this, out of force of habit.

 

[Catching Neutral]

I had a 79 that was completely desmogged / Trollhole carb.
Current 78, prior to Sniper, desmogged with OEM carb. Never had problems with either in the summer heat here in FL but have heard about so many who have.
Agree…Sniper will take care of it.

 

[AntFarm]

One of my 40's is a 3/79 with all of the factory emissions still in place. This truck is tuned per the FSM and runs really well. The carb fan only works about 50% of the time when I shutdown the engine, regardless of outside temperatures, or engine temperatures. (I still need to troubleshoot and fix this). This condition has created an interesting test environment for how much a carb fan helps with hot/warm starts. There is a consistent difference. A hot start when the carb fan HAS NOT run results is pulsating acceleration for about 1/4 mile before everything smooths out. A hot start when the carb fan HAS run results in a smooth idle, and smooth acceleration, in all weather conditions. My other 40 is a 9/74 with no AI, or EGR, and (of course) no carb fan. It never has any problems with pulsating acceleration after a hot start. My theory is that all the extra heat that is put into the engine bay, especially close to the fuel lines and carb by the Air Injection and EGR systems causes the vapor lock issues. If you have AI and/or EGR systems in place and running, then a carb fan really helps. If you're desmogged, then the carb fan really isn't necessary. Just my thoughts.

 

[85roktoy]

One of my 40's is a 3/79 with all of the factory emissions still in place. This truck is tuned per the FSM and runs really well. The carb fan only works about 50% of the time when I shutdown the engine, regardless of outside temperatures, or engine temperatures. (I still need to troubleshoot and fix this). This condition has created an interesting test environment for how much a carb fan helps with hot/warm starts. There is a consistent difference. A hot start when the carb fan HAS NOT run results is pulsating acceleration for about 1/4 mile before everything smooths out. A hot start when the carb fan HAS run results in a smooth idle, and smooth acceleration, in all weather conditions. My other 40 is a 9/74 with no AI, or EGR, and (of course) no carb fan. It never has any problems with pulsating acceleration after a hot start. My theory is that all the extra heat that is put into the engine bay, especially close to the fuel lines and carb by the Air Injection and EGR systems causes the vapor lock issues. If you have AI and/or EGR systems in place and running, then a carb fan really helps. If you're desmogged, then the carb fan really isn't necessary. Just my thoughts.

Your description is exactly what is happening. Pulsating acceleration for about 1/4 of a mile then she’s good. I have no carb fan AND it is desmogged so it’s still a head scratcher.

 

[Pighead]

What exhaust manifold do you have on it?

 

[85roktoy]

What exhaust manifold do you have on it?

Factory

 

[Pighead]

I only ask because, iirc, some of the later exhaust manifolds got very hot. The Thermonucular exhaust manifold comes to mind. I forget what years got those