north_curve Posted March 27, 2010 Hey guys I bought a 02 250f last year recent top end and recent overhaul of suspension sprockets chain etc so was running really nicely. A couple months ago I went to a big organized trail ride and started the bike up as usual let it warm up but when I went to ride it just bogged really bad backfiring etc. It still starts and idles fine. Anyway its been in the local yamaha mechanics for two months now and they just can't figure out whats wrong, first they re shimmed and adjusted the valves which probably was due to be done but didn't fix the issue. Next they decided it was the carb and replaced a needle and did some tuning still the same issue. They then tried a donor carb which didn't fix it. Now they think its the CDI unit but they can't find another one to try out in it as apparently only one from another 02 will work? Anyone know if other cdi's would work or have any other suggestions on what the problem could be? I have pretty much missed out on a whole summer of riding so I'm kinda pissed. Share this post Link to post Share on other sites
rcdude33 Posted March 28, 2010 That's really Weird bro. I don't have a yz but I read a whole bunch bout em. But did yamaha jet carb? Because it could be getting too much gas or maybe not enough gas. Also maybe check ur timing marks on your cams maybe they are off timing. How bad of a bog is it? Share this post Link to post Share on other sites
Toyota250f Posted March 28, 2010 has fresh fuel right? Share this post Link to post Share on other sites
north_curve Posted March 29, 2010 Yea they did play with the jetting and couldnt get it running right, i think its running lean, it basically idles fine but wont rev past what i would guess is about 3000 rpm and just has no power at all. I'm really surprised that they have no idea what it is after 2 months, are they incompetent? I've been thinking of getting it back from them and taking it to another mechanic. And yes it had brand new fuel when this happened. Share this post Link to post Share on other sites
gscx Posted March 29, 2010 The CDIs from 2001 to 2010 will work, they are basically the same engine. Share this post Link to post Share on other sites
BC3 Posted March 29, 2010 Typically if the bike ran good ONCE with the jetting in it, it should run good a year later with the same jetting (Jets don't change) That is is everything is clean... So I kinda would rule out jetting as a problem. What does the plug look like? How much cranking pressure does it have.....And does the bike back fire when you try to give it the throttle? I'm sure your shop has checked for all the normal stuff....Kinda weird that they have had it this long though....You might consider taking it to another shop Share this post Link to post Share on other sites
mike82 Posted March 29, 2010 your problem sounds like its electrical, in the magneto there is a sensor its small squared and black tell the guys in the shop to try the bike with a new one I think thats your problem Share this post Link to post Share on other sites
BC3 Posted March 29, 2010 Probably wouldn't start easy if it was a pick up coil.....I would get out your timing light and see what your advance sequence is like.... Share this post Link to post Share on other sites
BC3 Posted March 29, 2010 I just re-read your original post and noticed you said it did backfire......I would check the coil Share this post Link to post Share on other sites
BC3 Posted March 29, 2010 As mentioned it does sound like electrical.... Share this post Link to post Share on other sites
north_curve Posted March 30, 2010 Hey thanks for the suggestions guys, will give them a call tomorrow and see if they have checked the pick up coil. Share this post Link to post Share on other sites
