jonesy54

yeah, you don't have reeds in that motor, its just plain ole piston port induction.
how would the cracked carb body explain why it only does it when the engine is warm?

Does it get progressively worse as the engine warms up or does it run fine as long as it was cranked up cold?

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-1984 JS550 clone - restored, 440 pump, Skat Trak, primer, thumb throttle
-1987 JS550 - bone stock and staying that way for now
-1990 X-2 - the weird one

pwc hacker

When the engine is warm the cases expand you may have a cracked case.

98yota

The needle might be worn and letting too much fuel flow in. When the carb was rebuilt, was the needle arm put in correctly? I was having similer problems with my 89 Wavejammer 500 (which has the same Mikuni BN38 carb.) I rebuild the carb and found the needle arm was put in backward (little dimple was against the needle instead of against the spring.) It ran but was hard to start, even worse when warm. Switched the arm around during the carb rebuild and it runs perfectly now! I have pictures of what I'm discribing in my post "1993 WaveBlaster and 1989 WaveJammer project" found in the vintage ski threads. Hope this helps!

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1993 Yamaha WaveBlaster 701
1989 Yamaha WaveJammer 500

dodgetrucker75

I think the carb may be cracked because of the giant velosity stack that is on it, once its started it will run forever just fine, but once its shut down I have fuel leaking internally and externally from the carb with no clear indication where its coming from

tomegging

stuck float vale in the open position will run fuel all over as well. do you have spark when warm, if not, could be a bad coil. Coil resistance increases along with temperature. If you had a bad reed it would never run right even when cold.

Biscombe

Do you want the carb settings for the standard carb as it sounds like a flooding issue. You have a black engine the piston port type with no reeds. I have a 440 with a 550 engine in it. The restricter in the return pipe is when you remove the rpm limiter I think as you need to slow the flow of fuel so the carb can pressurerise I think