Jump to content

Poor yz250 not happy/ not wanting to start

Recommended Posts

Hey guys, picked up my 1996 yz250 a couple months ago and did a bottom and top end rebuild and i'm absolutely stumped, also fairly new to two strokes. The guy that I saved this bike from severely neglected it so its definitely a handful 

 

After doing my rebuild, i attempted to start it, and it ran about three different times they were all inconsistent and random when it started. I went on a trip for work for a week or so, and when I came back it wouldn't start, so I took the carb off and cleaned it and checked float height. It is completely clean and clear now. I reset the air/fuel mixture screw to recommended at 1 and 1/2 turns out. Still didn't start. So I changed the plug, nothing. messed with the mixture screw a little bit more. nothing. I also set the tuner on top of the choke to a middle position. Its got really good blue spark. I'm running 32:1 ratio just like the manual suggests. My main guess is that its a fuel issue but still no idea what that issue is. Super confused at this point. I went ahead and ordered a rebuild kit. 

 

Would the throttle cable adjustment at the top of the carb be causing this issue? Ive adjusted it a couple times just out of curiosity but it didn't change anything. 

The thing just wont start now. Thanks.

Share this post


Link to post
Share on other sites

Check the timing is set correctly?make sure the crank keyway is in place in the flywheel?is the plug getting fuel?just some ideas

Share this post


Link to post
Share on other sites
Just now, mudmixer said:

Check the timing is set correctly?make sure the crank keyway is in place in the flywheel?is the plug getting fuel?just some ideas

I will check about the keyway tomorrow, and the plug is getting fuel because it is slightly wet when I pull it out. Timing im not so sure on how to set, i just put the stator and flywheel back to where they were before.

Share this post


Link to post
Share on other sites
7 hours ago, Cbias said:

I will check about the keyway tomorrow, and the plug is getting fuel because it is slightly wet when I pull it out. Timing im not so sure on how to set, i just put the stator and flywheel back to where they were before.

You have to use a dial gauge indicator. The casting marks on the cases aren’t accurate and it only takes a few degrees advanced or retarded and the bike won’t run. I’d start there.

Share this post


Link to post
Share on other sites

Ok thanks man, I’ll be sure to look Into that after work. I’m also gonna chuck the carb into an ultrasonic cleaner just for shits and giggles while I work on the timing. 

Share this post


Link to post
Share on other sites

If that engine design has a 'windowed' piston, confirm it's facing the right direction. (intake side)

 

If in doubt, remove the exhaust pipe and have a peak up thru the port,

cycle the kickstart lever to move the piston up/down.

If 'windows' are visible in the piston's skirt, it's installed facing the wrong direction.

 

piston.jpg

Edited by mlatour

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:


×