Polaris 2001 magnum 500, oil and a very light smoke is coming from hose entering left side of airbox, nothing from right side hose, what could be the problem? oil level is perfect, never flipped the atv, runs perfect, until the air filter gets saturated with oil.

 

Left side is the crank case vent and has a big breather filter inline. Replace the filter or blow it out along with the line.Oil can accumulate over time in the filter and line and spray a mist inside the air box. The other vent is from the top of the oil tank and usually not a problem.

 

The breather is new, just installed it and started it up within 5 min. getting oil blow back.

 

Ok then look at this pdf break down on the 500 engine.https://www.google.com/url?sa=t&rct=...ZN9jLa7SAHw2aI Look at chapter 3 page 12. Shows the oil flow chart along with the one way check valve. Chapter 3 page 32 shows how to remove the check valve,spring and clean the valve plus the case needs to be clean where the valve rides.The valve is suppose to stop oil from the oil tank from draining back into the engine. If the valve is dirty/sticking,excess oil can enter the engine and crank case pressure can blow it out past the filter into the air box.Only a little over a cup or so of engine oil is in the crank case as it's running. Oil cycles through the engine then into the oil tank.Back and forth.The majority of the oil is stored in the remote oil tank.

 

yea, I have a shop manual and oil flow, I replaced valve and spring with new oem parts and still blows oil.

 

Ok,if you sure the check valve isn't sticking then sounds like you need to do an engine leak down test. Possible that you have too much ring blow by and if it does, air can go straight into the crank case and out the vent tube if it's leaking bad enough.