I just bought an 09 yz250 and aside from riding it in my yard i havent ridden it. I can get it up to about 3/4 throttle in 2nd. And noticed that it smokes constantly, more than normal. It has great compression. But was thinking that it may be getting a little bit of blow by so was going to change the rings. Not sure if i should put a topend in it or not

Also what is the stock size sprockets on an 09 yz250 and an 05 yz250?

Edited by LAYZ71, 15 July 2012 - 12:20 AM.

Have you done a top end since you have owned it? Was the first thing i did to my YZ once i brought it home. Just to make sure everything is in spec and all good.

I would suggest the same, then work on your jetting.

That said though, only being able to get up to 3/4 throttle in 2nd is not really accurate testing.

Constant smocking could be jetting, a dirty oil filter or the crankshaft's oilseal (wet side) Its a bit early to tell but if the previous owner raced the bike pretty hard chances are that your jetting is well off. Riding style is a quite a factor in jetting.

The stock gearing for my 2006 YZ250 was 14 front and a 50 rear. If you have the time, go through the engine, depending on how many hours the bike had put on it before you purchased it.

sounds like its smoking more than normal because your riding it in your yard and not even leaving second. But like others said, it wouldn't be a bad idea to go through the top end to make sure everything is in spec/ go through power valve.  Also, the bike will run a little richer with the hotter whether

The guy who had it before me was an older beginner. I had seen the bike ridden and he barely got the bike past 1/2 throttle. The only reason it hasnt been brought and strung out yet is the weather has been nothing but rain rain and more rain.

I think it could well be that your crank cavity is full with fallen out premix. IMO a half an hour ride better an hour with half to full throttle and you could be good.

I'd bet you're not able to get the bike up to full temp. putzing in the yard. No thermostat and these things warm up slow. Rich jetting makes it worse. Don't worry yet. Try the bike in you're riding enviroment before tweaking.

Theres a big spillway off the river full of sand about an hour from my house im goin to try to go to tomorrow and open it up if it isnt flooded. Thinkin maybe some major carbon build up in the pipe and silencer.

Well i didnt get to make it to the track, but i finally broke down and took the bike down the road. So i cranked her up did a few passes up and down the driveway to warm her up a little. Pulled out on the road and pulled it up to 4th pinned. Got about a 1/4 mile down the road pulled off and reved a couple times to see i it was still smoking. Noticed that the smoke had dramatically decreased but still a little more than usual. Turned around did the same thing pulled in at home and did a few more revs and other than at idle she barely smokes at all. Guess it was just some carbon that needed to be blown out of the exhaust system.