1. Float adjustment. The most common cause of gas in the oil on this model is a worn or damaged float needle in the carburetor. This can be adjusted by disassembling the carburetor and replacing the float needle assembly.
2. Vacuum line. Check that the vacuum line connecting the fuel pump to the carburetor is not cracked, torn or loose. Any leaks in this line can cause fuel to be drawn into the crankcase.
3. Fuel pump diaphragm. A damaged fuel pump diaphragm can also cause gas to be pumped into the crankcase. Disconnect the fuel line and use a low-pressure air hose to blow into the fuel pump. If you can hear air escaping from the crankcase or oil drain, replace the fuel pump diaphragm.
4. O-ring. The O-ring on the clutch side cover gasket can also leak and allow fuel to enter the engine oil. Replace the O-ring with a new one.
5. Check the piston rings and cylinder walls. If the engine piston rings are worn or the cylinder walls are damaged, this can also cause fuel to enter the engine oil. Remove the cylinder head and check the piston rings and cylinder walls for damage. Replace any damaged components as necessary.
Note: If you are unable to perform these repairs yourself, it is best to take your ATV to a qualified technician.
