I have had that situation happen with me a few times over the years. The problem that i found was a small blockage of debris somewhere in the carb. I cleared it by removing the air cleaner, starting engine, rev it up a couple times,then rev it up to around 2500 rpm and close off the carb air intake with a rag. Then open thottle wide open until the engine stalls.restart engine,you may have to hold throttle open initially to clear fuel out of the intake before it will start.reset carb air/fuel mixture and curb idle. The vacuum created by stalling eng out at high rpm generaly will pull out the blockage. Ive done this with other carbs with decent success. Change filter and also make sure fuel can is clean.Also if your timing is correct etc, and it been awhile since points and codensor have been changed, might want to give that a try..i gotta long story about that ...another day i know there can be more to look at, just a couple basic things to look at/ think about.
