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Sounds strange but you might want to check your float bowl level.
I had the same problem, couldn't figure it out. Bent it a little to raise the float height and was good to go.
Worked for me

Having this EXACT issue....makes stopping at red lights nerve racking!

This thread has some good, albeit confusing places to start!

Thanks guys!

is it a problem that crept up or did you change something ?

if you changed something, say rebuilt the carb the pump could be stiff in the boar or the spring is too tight. if it crept up it could have come from a gummed or coked up throttle pump piston.

some trouble shooting philosophy's: if you think its the carb its an electrical problem.
if you cant fix it with a hammer it's an electrical problem.

RMS wrote:is it a problem that crept up or did you change something ?

if you changed something, say rebuilt the carb the pump could be stiff in the boar or the spring is too tight. if it crept up it could have come from a gummed or coked up throttle pump piston.

some trouble shooting philosophy's: if you think its the carb its an electrical problem.
if you cant fix it with a hammer it's an electrical problem.

Haven't changed anything for a couple of years since the re-build of the engine...BUT to be fair, I haven't had serious driving just idling till now. Now that it is registered, I'm coming across this issue every time I go out!

I was thinking about throwing some seafoam in and letting it run through, think that would help this problem?
When I re-start the truck after this happens, it smokes like it was flooded...


The trouble shooting sounds spot on!
I had a starter issue and was walking towards the truck with a hammer. My girlfriend was screaming "NO! Tom! Dont break anything!" then I wailed the starter a few times and it worked perfectly...she was speechless!

-T

I would first pull the top off the carb and see if there are any issues with the pump or piston.
I recently rebuilt a carb for "Dark Green Canadian" and the new pump was tight in the boar I hooked up my vacuum pump, it took over 10lbs to get her to move. the assumed stock pump had huge clearances to the boar and worked like a champ, zero off idle stumbles.

I think I've figured out how to mitigate this for now....I idled the truck up just a touch on the throttle, and was really smooth with my acceleration.

RMS: Could I remove and plug the vacuum line for the wipers and solve this issue?

RMS wrote:I would first pull the top off the carb and see if there are any issues with the pump or piston.
I recently rebuilt a carb for "Dark Green Canadian" and the new pump was tight in the boar I hooked up my vacuum pump, it took over 10lbs to get her to move. the assumed stock pump had huge clearances to the boar and worked like a champ, zero off idle stumbles.

I think we are on different pages... when I did the test mentioned above I had the carb on the bench with the top off. I used a large plastic syringe with the same id as the throttle pump piston boar ( located on the top cap of the carb). with the throttle pump in the base, piston in the syringe, the syringe pressed down on the base holding down the spring and the vacuum pump connected to the pointy end of the syringe I was able to simulate the action of the throttle pump.

pwrwagonfire wrote:RMS: Could I remove and plug the vacuum line for the wipers and solve this issue?

If you have the wipers connected to the manifold you could have a large vacuum leak. witch may add to off idle stumble. run a vacuum gauge instead of the drivers side wiper and go for a run its a good way to see how every thing is working and it works well as a fuel miser

So what we want is the piston to have good clearance in the bore and not tight clearances? I remember having to press down to get the top of the carb on... I need to take it back off and check for smooth movement then.

the piston should have minimal clearances and move smoothly in the boar of the top cap. the throttle pump plunger that rides in the boar of the base should be sloppy with lots of clearance. the resistance felt during installation of the top cap should be from the spring on the throttle pump assembly and not the plunger or the piston.