A problem can occur if the thickness of the PLUG VALVES under the float needle valve is incorrect, which in turn will make the fuel level in the carburetor float bowl incorrect. The fuel level effects the fuel level on the emulsion tube. The emulson tube works with the air bypass jet and seems to effect the rate of fuel vaporization. This means that the level of the fuel in the carburetor bowl is critical.If the fuel level is a little low in the bowl (washer too thick), then facing downhill and cornering will cause the engine to run lean, causing stalling. Facing uphill the mixture would be a little richer