77 M880 Won't Stay Running When Warmed up Under Load

[twilli]

Can someone give me a check list of things to look at for this condition? The truck runs good on start-up but, after complete warm up, stammers and dies when trying to sit and idle in drive or reverse. I have to keep one foot on the throttle to keep it running when coming to a complete stop in gear. Here is a list of things I have done to the truck:

1. Carburetor kit put in
2. New plugs and wires installed
3. New vacuum advance installed
4. Checked and repaired all vacuum lines
5. New rotor and cap
6. New fuel pump and filter

It has a 318 with factory carburetor.

Thanks,
Todd

 

[Digger09]

Vapor lock?

 

[Scar59]

Vacuum leak some where, mounting plate gasket?

 

[NDT]

Maybe fuel starvation. The in tank pickup may have rust holes allowing air in instead of gas. See if you are getting a solid stream of gas from the pump when you crank the engine after a stall.

 

[Amer-team]

Did you replace your rubber fuel lines from the tank to the fuel pump? I had a similar problem and there was a short piece of hose on top of the tank that ended up being cracked and drawing air.

But will say that if I let it sit for a month or two, it loses prime. Once primed and if I run it every once in awhile, runs and starts great.

 

[Bob H]

after complete warm up, stammers and dies when trying to sit and idle in drive

What is the idle speed in park once fully warmed up, choke fully off? in park?
Can we assume it stays running @ idle in gear when cold and the fast idle is active?

 

[twilli]

What is the idle speed in park once fully warmed up, choke fully off in park?
Can we assume it stays running @ idle in gear when cold and the fast idle is active?

Idle is a bit high when warmed up, choke off and in park.
Yes, it does stay running when cold even without fast idle active.
Thanks for the reply.
Todd

 

[twilli]

Did you replace your rubber fuel lines from the tank to the fuel pump? I had a similar problem and there was a short piece of hose on top of the tank that ended up being cracked and drawing air.

But will say that if I let it sit for a month or two, it loses prime. Once primed and if I run it every once in awhile, runs and starts great.

I replaced one that looked like it was constricted along right side frame rail. I also replaced the hose that runs from the plastic canister on top of the fuel tank because it had a crack in it.

 

[twilli]

What is the idle speed in park once fully warmed up, choke fully off in park?
Can we assume it stays running @ idle in gear when cold and the fast idle is active?

The idle speed is somewhat elevated when fully warmed up and the choke is off in park.
Yes, is does stay running at idle in gear when cold and the fast idle is not active at that time. It acts fine when it is cold.

 

[bikeman]

have you replaced the resistor/ceramic thing under the hood?

I was having a similar issue, but **** if I remember how we fixed it.

 

[Eaglhawk]

1) Check timing
2) Carburetor rebuild not cleaned properly -
I always had problems rebuilding the old carbs on these 318's and 360's. You can use solvent to clean them
but that never fixed the metal oxide build up on the internal pathways from years of oxidation due to moisture
corrosion. I finally worked a simple solution... Note: DISASSEMBLE all removable components from the various bodies. First clean the bare bodies with standard solvent from any autoparts store. Then after all organic material is removed and rinsed, submerge the carburetor bodies in a solution of around 180f CLR from any walmart or supermarket... (cleaning supplies). WARNING!!!! This solution can dissolve away the carburetor if left in for too long. move it around in the solution to allow the solution to penetrate the inside pathways. It will bubble a bit while it dissolves the oxides plugging up the inter pathways. Usually 5 to 10 minutes will do the job and open up and smooth out the pathways.... Rinse it thoroughly, dry it quickly, HOT, with a blow drier to drive out any solution from inside. Then spray WD-40 on the inside to keep any more oxides from forming before it is put into service.

3) (Hard-must drop gas tank) Filter on fuel pickup line inside gas tank is nearly plugged with shellac or stuff. This filter can be vary problematic causing various issues. I found it best to remove the filter from the metal pickup line and replace it with a custom one (same basic shape) but made with window screen. This only stops large particles that could plug the fuel line. Then next to the frame of the truck where the metal fuel line from the tank goes through the frame I add a generic inline fuel filter from any auto parts store. (This allows super easy replacement should filter get plugged from dirty fuel) This mod fixes a lot of weird issues caused by that fuel pickup...

 

[michigandon]

We went through several re manufactured Carter BBDs recently anc couldn't get any of them to run quite right. Finally gave up and went with a Rochester. Runs like a scalded dog now!

Alslo had lots of problems with junk in the Fuel system, despite our best efforts to hose out the tank. Solution was to install a 10 micron Racor marine filter in the system. There is a small section of rubber hose about halfway up the steel line that makes a perfect spot to splice one in. Mount the filter istelf on the frame rail.

 

[snowtrac nome]

I would suspect low idle, a carb problem vacuum leak, should be around 18 inches at idle, plugged idle bypass port, you adjust idle bypass with lean idle drop than back out 1/2 turn, or secondary ignition miss fire. If your timing light is jumping around suspect a timing chain I would think by now all the plastic cam gears should be gone but one never knows.

 

[440Duster]

Check the operation of your choke. I have one truck with the electric choke mechanism and one with the bi-metal spring. The electric one works fine but the spring one doesn't work correctly. The choke plate doesn't open mimicking what your truck is doing.

 

[snowtrac nome]

Check the operation of your choke. I have one truck with the electric choke mechanism and one with the bi-metal spring. The electric one works fine but the spring one doesn't work correctly. The choke plate doesn't open mimicking what your truck is doing.

If the bi metal choke isn't working it is because the exhaust cross over is plugged up. All Chrysler v-8 of the time suffered this problem, but seemed more problematic with the small blocks, sometimes the intake had to be hot tanked to clear the carbon causing the obstruction.

 

[Karl kostman]

I dont know a lot about these vehicles but if it starts good but runs like crap or stops running when the engine gets warm it could also be a coil, when they get hot and are going bad this is a lot of times what happens. Let the truck sit for an hour and let things cool off and it will start right up again.
Karl