- Breather tube blockage:
The breather tube is attached to the top of the engine, and it allows excess fumes and oil vapors to escape from the engine. If this tube becomes blocked by dust or debris, the pressure may cause the oil to spit out of the air cleaner.
- Worn piston rings:
Ensure the piston rings are seated correctly and not damaged.
- Excessive oil:
Make sure the oil level in the engine is not too high. Overfilling can cause the oil to be sucked up through the breather tube and into the air cleaner.
- Incorrect oil viscosity:
Using an oil that is too thin can cause it to be more easily blown out of the engine by the combustion gases.
- Sticking float valve:
A float valve that is not allowing the correct amount of fuel into the combustion chamber might cause the mixture to be too rich, which can also cause oil to be spit out of the carburetor.
- Clogged jet:
Check that the jets in the carburetor are not clogged, as this can cause the fuel mixture to be too lean, which can lead to oil spitting.
- Over-tightened head bolt:
The head bolts that hold the cylinder head in place should be torqued to the correct specification. If they are over-tightened, it can cause the cylinder head to warp, which can lead to oil leaks.
- Failed gaskets:
Inspect the gaskets between the cylinder head and the cylinder block.
- Failed or missing gasket:
Check for a proper gasket between the carburetor base and the air cleaner. An old, worn-out or missing gasket may permit oil to be drawn into the air intake.
- Incorrect size main jet:
Incorrect main jet sizing may cause the engine to run rich causing fuel to be pulled into the air intake.
- Dirty air filter:
A blocked air filter may create enough restriction to cause the carburetor to draw oil from the crank case.
- Failed or loose oil drain hose: Check for a loose or damaged oil drain hose that directs oil from the air cleaner back to the engine crankcase.
- Oil pump:
A weak oil pump may not produce sufficient oil pressure allowing oil to leak from the air cleaner.
