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1981 cm400A. new piston rings, new plugs, carbs clean, pod filters, straight pipe exhaust (rejetted with 78 and 138), good fuel and oil w filter. the bike will start right up and run AMAZING but after about 20mins of riding it will have no power, won't go above 40mph, and won't idle. doesn't matter if you are riding steady or doing stop and go in town. it has plastic floats so i can't adjust fuel level. after it starts acting up i pull over and there is a little white smoke coming from around the spark plug. all i have to do is kick it and give it throttle and it will run but it has no power and won't idle. if i let it cool down for a while it will start back up and run like a champ again. is something electrical getting hot?

Check your fuel tank vent.

i rode without cap yesterday. went 14.2mi (about 23mins) and it seemed to do fine. even let it idle in garage for 2mins. thank you very much. i never would have even guessed that was an issue

@JohnJ, you da man

it still dies a little bit. i think it's getting too lean and hot while riding. i adjust the idle screws out (it has open exhaust and pods). i even applied rubber sealer around pod boots to make sure it wasn't sucking air where it shouldn't. could the lean condition cause it to get hot and then shut down?

If it has open exhaust and pods on it, it needs to be rejeted.

for care and giggles check your valve adjustment if applicable.

i did re jet it. think my main could be one size bigger though. i will check valves soon, it's been on my list

What's the stock jetting and what altitude are you at?

Are the straight pipes new to the bike?