The battery is fine, and the engine cranks, but the bike won't catch and start idling. If I hold the throttle the bike will run, but as soon as I let off the engine cuts off.

Basically, I give it throttle to start, and it does, but as soon as I let go the engine stops. I know the carbs need to be cleaned, and will be doing that shortly, but I wanted to ride the bike around a bit, because I just got it. Is the problem because of the carbs, or could it be something else?

 

Have you tried to see and check the idle screw?maybe it's set too low, so it won't idle when you let the throttle off. Try to turn it clockwise to make the idle higher and vice versa.

Clogged pilot jet might be the other cause as well...as this' part that works for idling.

 

So you're saying it will run and rev up as long as you don't completely let off the throttle? That to me sounds like the idle stop isn't adjusted properly, just like K4y_d1 said.

 

yeah probably just set too low... at the very least adjusting the idle stop to a higher RPM will keep it running long enough for you to run some seafoam through the engine to clean out the gunk if the pilto jet is getting clogged up.

 

idle circuit, float height, wrong sizing of needles and jets. The comment on having the idle screws is true as well. Go back to basics, and find out where your carbs are at.

 

carb sync nozzles on the intake boots, sonetimes the little rubber caps dry rot and seap air