Why is There Soot in My Polaris ATV Airbox?

Got a Polaris ATV with a dirty airbox? Your ATV might be experiencing what’s known as engine “blow-by”, and you may need to replace the cylinder and piston rings.

Partzilla’s Polaris ATV expert John Talley livestreams Q&As on our YouTube channel every Friday at 3pm Eastern. In this session, John addresses what could be causing black soot buildup in the airbox of a Polaris Sportsman 450 ATV.

Polaris Sportsman Dirty Airbox Problem

I’m working on a 2006 Polaris Sportsman 450 and there’s a lot of black soot buildup in the airbox. I think it’s coming from the air line coming off the motor. What can I do about that?

John Talley: What’s probably going on is the breather hose for the crankcase runs up to the airbox, because it’s got a vent somewhere. Any internal combustion engine is not 100% efficient as far as your ring sealing, so a little bit can go past the cylinder, or past the piston and rings, down past the cylinder and into the crankcase. But what’s happening with yours is that it’s getting excessive and you’re getting a lot of what they call blow-by. And that’s forcing its way past the piston rings, going into your crankcase going into that vent, into that tube and then back up into the airbox. Yours is evidently pretty severe. If you want to see just how severe, why don’t you open up the — this may make a bit of a mess with idling — just open up your dipstick in the side of the engine and see if it’s spitting oil and air, combusted air out the engine. Now, if that’s the case and you’re going to fix that, you’re going to need at least piston rings and a new cylinder to straighten that back up. Sorry to be the bearer of bad news, but if you go through this process at least not only is it going to clean up your airbox, but your machine is going to run a whole lot better …

Watch the video below to see how to replace the piston and rings in a Polaris Sportsman ATV engine.

Want to see more live repair questions answered? See more motorcycle and ATV repair questions answered here.