What causes momentary revving

[Holyman]

I just bought a HOnda CT70 scooter from a guy I went to grade school with. It's in really graet shape and doesn't have hardly any miles. But the friggin thing will run at idle just great and then all of a sudden it will rev up to about 1/2 throttle for about 2 minutes and then it will gradually go back to idle and then almost stall and then after about 10 minutes, it will do it all over again.

Is that an air leak? Or float height not right?

[locogato11283]

sounds like some sort of lean condition. most motors will rev up when they are about to run out of gas but for 2 minutes doesnt seem common..i would pull the carb apart and clean it and what not. if that doesnt solve the problem you could have an air leak. of course you could check for the air leak real quick using some starting fluid(not too much of course). it sounds to me like its starving for gas...

[RATBIKE0130]

I just bought a HOnda CT70 scooter from a guy I went to grade school with. It's in really graet shape and doesn't have hardly any miles. But the friggin thing will run at idle just great and then all of a sudden it will rev up to about 1/2 throttle for about 2 minutes and then it will gradually go back to idle and then almost stall and then after about 10 minutes, it will do it all over again.

Is that an air leak? Or float height not right?

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Sounds more like it's vapor locking.

[ssanddemon]

Congrats, those old Honda bikes are real durable. Sounds to me like either a piece of crap floating around in the float bowl occasionally plugging up the main jet or water in the float bowl. No matter what, I would pull off the float bowl. Maybe another idea is to see what fuel flow looks like with the fuel line off and then fuel valve turned on. If it is a wimpy trickle, you may have a plugged fuel filter or in-the-tank-strainer.

[Holyman]

I kind of figured it was a carb issue. I'm looking forward to getting it running well. It is a 1980 Passport 70 and only needs a few things to really look like new. There's only a couple minor rust spots on it from a couple rock chips in the paint. Otherwise it looks like new. It's been aound 15 years since my last 70cc Honda. I still say my old atc90 was one of the funnest machines I've ever owned.