2002 yz 125

[A-310]

Been chasing a snag on my bike now for a week. Wondering if anyone has had any similar problems? I've put about 10 hours since I bought the bike and it has been running well for about 7 hrs, but started having problems. The bike will run well, then just quit like I turned the ignition off. No mater what you do while still motoring to a stop, the engine will not relight. After coming to a stop, the bike will start first kick, run well again and do the same thing again but not regular. Take the plug out and it is rich , wet but no carbon. I chased the coil wiring and sanded all the coil connections and wiring seems fine. Ran the bike again and same thing. Took carb off and checked for loose crap in float bowl, nothing, it was totally clean. Put carb on and ran again same thing. Changed plug cap and ran again, this time ran better as old cap was loose. Ran really well for an hour then quit again. Took fly wheel cover off and cleaned magneto and related gear. Resealed the cover and ran the bike again, ran well for an hour and started giving trouble. Put more fuel in and added more oil to simulate a leaner mixture. Cleaned the plug, which by the way are new, and gave it another go. This time it ran perfect and never quit again, ran about another hour. Took plug out and it was a little leaner, but still too rich. Main jet is a 420 and going to go down to a 400 and see what this will do. The conditions are 34 degrees Celsius and 80% humidity. I'll see if the problem re-occurs the next time I ride. What's your take on this? Usually fouled plugs start missing then die, not restart and run well till the next foul? As well after the stops became more frequent, I would put bike in neutral and add full throttle and engine would quit and start again first kick? As well it will only do this when you've been on the pipe, otherwise it never quits.

[Blitz393]

it sounds like a rich main jet and a perfect pilot jet.. hence the easy starting. go to a 400 main and see what that does. if it helps, go leaner (in smaller steps!) and get until it runs just a little too lean, then go 1 size above that.

Rob

[A-310]

I changed the main jet which was a 420 and now it's 390. Runs really well, with a huge increase in power. The plug now is brown, so the mixture is just about right. I took the carb apart and cleaned and blew out all the circuits, but the carb was clean. Checked the flow from the tank which is good. So I put the carb back on and ran the bike. It ran sweet and I could not get it to quit. I ran the piss out of it for two hours and no trouble. Thought I had this one fixed? But after cleaning the bike I thought I would try full throttle in neutral and see if it would quit. It runs for about one minute and shuts down. Starts first kick and go half throttle no problem, 3/4 throttle and more for 1min and it quits. So I had to go, so the next time I go out I can now check the plug after it quits. If its wet its ignition, and if its dry its fuel. I have a feeling it is the coil braking down at high rpm for a certain time period. It's got so much power now that I can't keep it on the pipe that long as the track is short, so it never quits with the short bursts of power. I'll get it nailed the next ride. What I could not believe is the change in power by leaning it out, wow it should kick most bikes at the club. That's if I can stay on the bloody thing?? Take care

[souphmars]

i have an 03-i live in tennessee-i also run a 390 year round with no problems at all-

[Woodsie]

Might be the CDI. I had the same problem on a 4 stroke Honda.