Grubee GT4

[TomatCP]

Hi ive had a grubee GT4 engine which runs well but at full throttle it hits about 26-27 mph (bike speedo) and then acts as if it is running out of fuel. The result is my top speed pulses from around 25-26 which sounds good and the engine can maintain but above that it acts like its out of fuel. I thought it may be too small of a main jet so i bought bigger jets but the problem doesnt seem to be fixed and im running out of options. Anyone experience this/can you help?

 

[GearNut]

I bet it is running too rich. What color is the spark plug? Black= too rich, white= too lean.
Chocolate brown to leather brown= perfect.

 

[LuciferJesus]

Haha.. Same thing happened to me. Vibrations were making the fuel in the carb bowl foam. Fuel starvation ensued. Took off makeshift rubber mounts. Installed makeshift leather ones. Vibration was lessened. Symptoms went away.