Series III surging

[REDrum]

The second....pushing down then letting up...bucking would have been a better description.

Thanks, that helps!

[raleighrover]

Update: I replaced the original fuel pump with a new aftermarket one. The truck ran well for a bit, but then the new pump started leaking gas into the crankcase. I replaced it with another new aftermarket pump (and changed the oil!), and it's been working pretty well. When cold, the truck starts great and runs really smoothly. However, when the engine is warm it's much harder to start. It almost acts like it's flooded - I need to give it a lot of throttle to get it to fire, then it will only run on a few cylinders for a few seconds before it smoothes out and runs well.

It used to start just fine when warm or cold, so not sure what's going on. Could the fuel pump affect the way it starts when warm? Any other ideas? the pumps are the only thing that has changed.

[erik88lr]

Update: I replaced the original fuel pump with a new aftermarket one. The truck ran well for a bit, but then the new pump started leaking gas into the crankcase. I replaced it with another new aftermarket pump (and changed the oil!), and it's been working pretty well. When cold, the truck starts great and runs really smoothly. However, when the engine is warm it's much harder to start. It almost acts like it's flooded - I need to give it a lot of throttle to get it to fire, then it will only run on a few cylinders for a few seconds before it smoothes out and runs well.

It used to start just fine when warm or cold, so not sure what's going on. Could the fuel pump affect the way it starts when warm? Any other ideas? the pumps are the only thing that has changed.

Could be that it is literally flooded. I recently had to replace my Zenith carb float because one of the two chambers was half full of fuel.
Another factor could be vapor lock caused by the ethanol in the fuel sold these days. You might true a tank full of pure gasoline. See https://www.buyrealgas.com/