Joined: Mon 10-11-2004 8:58AM Posts: 209 Location: Rolla, MO
Source: Fidelity
I just finished a rebuild on a Yamaha Tri-Moto 200cc engine for my buggy, starts and runs great, but when it warms up, it idles low and dies.
Tried adjusting the idle, but still does it.
The rings are seated well, its got plenty of power now, but it just wont stay running right after I let off the throttle and it goes back to idle. I am sure the idle circuit is clean, jets and pilot are new, and I cleaned every hole well. I've tried adjusting the air mixture screw with no success.
The new jets are stock size.
It did the same thing before the rebuild....
If you adjust the idle mixture screw and nothing happens, you most surely have a vacuum leak. Spray around suspicious areas with a can of WD-40 or carb cleaner, and if the idle goes up, you have a leak there. Carb base would be my first guess.
Joined: Mon 10-11-2004 8:58AM Posts: 209 Location: Rolla, MO
Source: Fidelity
A friend of mine suggested spraying the carb as well, if I get time I'll try that tomorrow. Still seems odd to me that it only does it when the engine is fully warmed up though...
I have found the best way to find a vacuum leak is to use carb cleaner instead of WD-40. Also, before going vacuum-leak hunting, lean out the idle mixture as much as possible. For hunting down vacuum leaks on my '72 Chevy pickup, which has always been plauged with them (despite its lack of vacuum and emissions hoses...), I would lean out the idle mixture until the truck was barely running at around 300rpm. A shot of carb cleaner anywhere and the RPM would jump to 800 or so, making it very easy to tell where your vacuum leak is.
Also, is the air cleaner on? This may sound trivial, but I've worked on several ATV and small power equipment engines where they will not run right with the air cleaner off. These include a 4-cylinder Suzuki motorcyle engine, a Honda Recon, and several Briggs and Stratton engines. For whateve reason, they are designed for the restriction and loss of airflow that the aircleaner causes, and will run lean with the aircleaner off, which could easily cause your problem. If your air claner isn't on, I'm willing to bet that its your problem.
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