throttle keeps getting stuck

[TuExplicit]

i have a yamaha 250cc from 1989 i changed the carb on it recently everything runs fine but sometimes in like 3rd gear the throttle will get stuck flooring it the handlebar goes back and forth its not the problem, i have taken the carb apart and cleaned it and made sure nothing is sticking in there i cant figure out why it keeps doing it it seems like nothing is stuck and i have triple checked but even when i start it up it just floors it

 

[dirt bike dave]

The throttle cable could be old and frayed inside the sheathing. Impossible to see from the outside. Cables are pretty cheap, and with a new one at least you can rule that out.

Its also possible that the slide and carb body are worn, and under heavy vacuum the slide is getting 'tilted' in the carb, and sticking.

 

[ellandoh]

could be that you like 3rd gear and its coincidence that the bike is getting starved for fuel, if the throttle and slide are smooth i would check jetting and float height

 

[High Lord Gomer]

I once had an RM (might have been 89) that the throttle would hang wide open on. It was because at full throttle the needle would actually clear the main jet and since the spring on top was loose, it would bounce to the side and hang .