motor runs for a block then wont accelerate

[arceeguy]

If the carb is upside down, the float should close off the needle valve, preventing fuel from entering the carb at all.

 

[AussieSteve]

Of course. I'm a bit slow sometimes. (I seem to say that more and more often these days.) The carb wouldn't be leaking, or at least, not much. Gravity might not seal the float valve as well as flotation, so it could have got enough fuel to start for a moment.
... Steve

 

[HseLoMein]

Maybe the carb was right and the airbox was put on upside down

 

[motorpsycho]

If the carb is upside down, the float should close off the needle valve, preventing fuel from entering the carb at all.

you're right. i was thinking backwards.
i was thinking that fuel would come out all over the place.
but, if you flip a carb upside down the float would be in the up position, acting like the bowl is full, and the needle & seat would be closed.
but if there was some fuel in the bowl BEFORE it was flipped upside down, the fuel that was in the bowl would leak out through the main jet.

 

[motorpsycho]

you need a vented fuel cap for this fuel system to work right because the fuel is gravity fed.
without a vented cap, it will create a vacuum in the tank, and no fuel will flow.
these caps are supposed to be vented, but maybe he got a bad one?

 

[AussieSteve]

Yeah, I had a good look at mine today. It does have a vent that should bypass the rubber. Hard to test if it works, though. An internal drilling in the right spot would probably ensure that they breathe OK.

... Steve

 

[Ryan b]

my bike is giving me problems. its struggles to start up sometimes but eventualy it starts and i ride for a block or two and the all of the sudden it wont accelerate any more. the motor is still on and it just doesnt go when i twist the throttle. i stop and try to start it again and it struggles to start but then eventually it fires up and rides for a few blocks and doest it again. ive never had a problem with the engine until now. its always been fine. i thought it was the throttle but the cable seems to be pulling the valve side in the caburator properly. im thinking that it may be a spark plug problem or too much fuel is getting into the combustion chamber and its flooding. any ideas would help. thanks

I would check your magneto. I gad the same problem and one of the connections broke.