Jump to content
Sign in to follow this  

Yz 250 fouling plugs and oil out over flow hose

Recommended Posts

Hey guys a recently tuned my carb. A 175 main jet and a 48 pilot jet. The air screw is turned all the way in. And the needle is on the 4th clip (2nd clip from top) im trying to get the bike to stop fouling plugs, it used to foul them super quick until I changed the needle position. When I turn the air screw 1 1/4 out, the bike idles really lean and choppy. And ive tried adjusting the idle on the choke and I still get the same thing choppy when the air screw gets turned out. When it in it runs fine I dont know why. When im riding the bike feels great and has awesome power. Im running 40:1 yamalube 2R in it. Also when I was riding today the bike splurged some thick oil out of the hose on top of the cases right behind the cylinder block by the reeds. Thats the first time it has done that. I believe its trans oil cause it was thick and kinda smelt like it, But it was purple like the oil I mix the gas with. About 2 quarter size drops came out of it and that was it. I dont know if that okay or not and that worried me because I dont know what that breather hose is for. I was thinking if I dropped the main jet to 172 and raised the pilot jet to a 50 and then do a plug chop I can go from there. The plug I have in there is a br8eg. The plug will last about 3 to 4 sessions of riding then wont spark anymore. I looked at it several times before i started each ride. It was a nice mocha color, then the top of the plug on the prong started to get black, then it started to get black on the inside and then wont have any spark to it. Im clueless. Any help would be appreciated! Thanks guy -ben

Share this post


Link to post
Share on other sites

Air screw in all the way is suspicious. The lean problem could be an air leak in your left side crank seal.

 

Oil pushing out the crank case breather is also suspicious.  You might have a leak in the right side crank seal.  The plug fouling could also be trans oil getting sucked into the crank case, and a droplet of oil fouls the plug.

 

If the seals are old or of unknown age, then just replace them. They are real cheap at about $10 each.   No need to split the case.  Check out the Rock Mountain video on youtube showing bottom end rebuild. If the seals should be good, then you could pressure test the case. Search TT for details.

 

If the seals are bad, then I'd be concerned about the health of the main bearings. So check for zero play in the mains and a nice smooth feel to them.

 

Plug fouling can also be caused by some types of fuel.

 

You said it sometimes runs great, so I'm guessing your air filter and exhaust are not clogged up.

 

Hope that gives you something to go with.

Edited by numroe

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×