Partzilla Live Q&A with John Talley – October 23, 2020
Partzilla’s John Talley sits down once again for another Friday afternoon edition of Live Q&A, taking on your motorcycle and ATV repair questions.
Partzilla Live Q&A Highlights – ATV/UTV Oil and Fuel/Air Problems
I have a Yamaha YXZ1000 I did the service on almost a year ago and I didn't use it. Does it need to be serviced before I use it again?
John Talley: As long as you didn’t run it a long period of time, it should be ok. But what does happen when you set up a machine that has been run a fair amount is that the oil has contaminants in it and they’ve just been sitting in that engine the whole time. And maybe they’re starting to eat your bearing surfaces because as oil gets used, it really has to start working, it starts getting impurities in it and then it’ll actually become acidic if you can believe that. So let’s see, having to rebuild an engine or just do another oil change? I think I’m going to go for the oil change. Would it probably be ok? Yes. But if it’s been sitting up for a year, go ahead and drop it out and start with fresh oil for the season.
I rebuilt the top end of my Honda TRX 350 and it’s running rich, to the point of a new spark plug turning black after only running it a few minutes. Any advice?
John Talley: Hmm, rebuilding your top end shouldn’t change your air/fuel mixture coming into it, so I’m a little perplexed by that. I would want to go back and just verify that your timing is correct, so if you would, take a peek at that. … Other than that, something must’ve changed in the carburetor for it to be running so rich. Check your timing first and then go back in your carburetor to see if there’s something going on in there. Maybe an air/fuel setting on the side of it. Maybe that screw got turned not by you but maybe somebody else when they saw the carburetor sitting on the side of the unit. …
I have an 05 Polaris Sportsman 500 and it’s running very rich. The enricher doesn’t work, and I have an erratic idle and oil in the airbox. Would it be a choke adjust or a jet adjust?
John Talley: Well, you gave me one little thing that shouldn’t be going on. It’s spitting oil up in the airbox, and that indicates to me that you’re getting a lot of “blow-by.” Blow-by is when your rings and/or your piston within the cylinder walls become worn and you’re letting too much compression escape past the cylinder, and it’s actually building up pressure in the engine cases and that’s gotta go out through the vent. And the vent goes into the airbox, and if there’s too much pressure in there it’s not just going to release the pressure of the gases in there, it’s going to start spitting oil. But before you jump to conclusions, make sure that your oil level is correct to begin with, because I know with certain Polaris’s it’s easy to overfill them and they start spitting back in there. If you’re sure that your oil is correct, you may want to do a quick compression test to see if it falls into range …
Want to see more live repair questions answered? See all of John’s Live Q&A sessions here.