81 Ironhead, stock carb, just got it all road ready and am wrapping up a few odds and ends. When driving at a constant speed she'll start popping out the carb, stop for an amount of time and then start again. Sometimes you can go several miles with no problem then it will pop 5-10 times and then run OK again. Other times it goes 100 yards, pops, goes another 100 yards, pops again and eventually settles down. This is with a warm engine. It DOES NOT pope at WOT or when it's accelerating. It pops with the choke on as well. With the choke on when you take off cold it feels like it's running out of gas. Float level will be checked tomorrow. Any suggestions? I had one guy at the local indie shop tell me coil or ignition module. I suppose it could be cutting out and back in. It almost seems that way.

 

you have a vacuum loss at that throttle location

 

FWIW, I had a similar problem with my '82 a couple summers ago. It would accelerate up to speed with no problem, but once I reached the speed I wanted to run at, my bike would stumble, run rough, and lose speed. I could twist the throttle and it would accelerate back up to speed, then the problem would repeat.

I pulled the bowl off my carb and found several small pieces of yellowish grit. I cleaned those out and haven't had any problems since.

I assume those pieces of grit were plugging up passages in the carb, starving the engine of fuel. Twisting the throttle would activate the accelerator pump, and it would accelerate normally.

 

I've found the most common cause of carb farts on Ironheads running the stock Kehin butterfly carb is too small of a low speed jet. If you have non-stock mufflers and air filter on it (which almost all do by now), you need to go up in jet size one or two sizes bigger than stock. Main jet should be made bigger than stock too.

The second most common cause I've found is the old centrifugal igntion advance unit being worn out. But it mostly gives carb farts at idle and low rpm.