This YS140 was purchased used and reported to be recently rebuilt by YS in Japan. The engine runs strong but has an idle problem. First, the engine must be turned over by an electric started to get fuel pumped up the carburetor. Hand cranking 10-20 times (with the carburetor open) will not get fuel up to the needle valve. This would make me think the crankcase pressure was low. However, after running the engine, there is a lot of pressure in the tank. The engine has good compression. When the engine is running and the throttles close to the idle position, the fuel line from the regulator to the carburetor is almost completely devoid of fuel. There a few droplets of fuel flowing from the regulator to the carburetor which is keep the engine running. When the throttle is advanced, this fuel line immediately fills with fuel. The idle will randomly vary about 300 – 500 RPM. which makes it impossible to get a reliable idle at the desired 2000RPM. The engine also seems to be spraying a small amount of raw fuel from somewhere around the carburetor. I have changes the regulator diaphragm, and plunger. No change. Any ideas?

It was probably not worked on by YS in Japan.

I needs to be sent to YS Service at this address:

YS Service
1295 Industrial Court
Gardnerville, NV
89410

Sorry for the headache.