Posts
388
Joined
6/30/2014
Location
Independence, OR
US
Just picked up a yz 250. I rode it on the test drive and it was smoking a lot, so I figured it was a jetting issue, no big deal. I got home, changed the transmission oil, did a top end, new plug, new filter, 40:1 and fired up the bike and it ran exactly the same as when I test rode it. Reeds look good. Starts okay and runs off the bottom okay, but then at 1/4th throttle it chokes up, sputters, and smokes like mad. I leaned it out a few times, clip position, main, and pilot with almost no discernible difference. I also adjusted the float level and checked the float with the bowl off. The float needle is working as it should. So I'm thinking maybe crank seals. I've never had an issue with crank seals, so I'm not sure what it typically looks like. I just pulled everything to get to the seal on the clutch side, and I can't see anything wrong with it. If it were a bad seal, would I normally be able to tell by looking at it? Is there anything else I could check on why my bike is rich?
I would suggest looking at the bottom side of the old piston to see if there is a dark deposit in it. If there is said deposit, then the clutch side seal is leaking, assuming as you stated that the carb is working correctly and your center crank halfs are sealed correctly and not leaking.
Paw Paw
The Shop
Not the side that it would get the oil from but Pull the ignition cover off and see if there is any up or down play. Worn main bearings could pull upward on seal letting some oils slip by.
Could be a leak from the yamabond between the cases too.
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