Starting Q, backfiring and fouling plugs. . .

[robbieisurfriend]

My YZ250 is fouling plugs quite often now. I will go through atleast a plug in a day worth of riding which is no bid deal really but sometimes when the plug is getting bad and I try to start it (flooded?) it will backfire. Im wondering if I should buy a gasket kit so that I can inspect the top end before I get a seizure. Is backfiring a really bad thing or just early signs of a problem? I am getting some spooge, (im not sure what a lot is), so it might be a little bit rich. It runs great once it gets started for the first time and as long as you dont stall it out and try to start it. The last owner told me the best way to cold start it and said that it will start 2nd kick everytime. He said to not use the choke, no throttle, and give it one slow kick to get it primed then kick the hell out of it and it will start. This doesnt work for me at all and I usually get it started only after getting it to almost bumpstart then kicking it. Even after it is warm I have to give it some gas for it to start sometimes. If you guys have any tips i would greatly appreciate them because it would save me alot of hassle. Sometimes I get it going with one hard kick but the majority of the time it is a pain in my ass. Oh and the problem is not my kicking, I take my time between kicks and give it, and my foot some serious hell. thanks.

 

[2strokerfun]

Sounds like you might be due for a new top end. I think your idea of taking it apart and inspecting it is right on target. Measure everything while your in there. Running a little rich will also cause the fouling, but shouldn't cause the starting problems. Of course, a dirty carburetor will cause the starting problems. I'd also take it apart and clean the heck out of it. paying close attention to the pilot and main jets.

 

[DougRoost]

Sounds to me like it's jetted way rich, especially if it supposedly starts easily w/o the choke every time.

Have you done a compression check on it? Compression gauges are cheap and the best way to quickly measure the condition of the top end (now and in the future). The seat-of-the-pants way to measure it is how much resistance you feel in the kickstarter, especially as it degrades over time. Since the bike is new to you that's not going to be of much use, unless it's really easy to kick (in which case do a top end job ASAP).

The good thing is 2 stroke top ends are cheap and easy with a decent manual (or Eric Gorr's excellent book). My advice would be get the full top end kit, since once you get it apart for inspection you might as well replace the piston and ring(s). Also be sure to clean, inspect, and adjust the powervalve mechanism.

 

[robbieisurfriend]

From what I have felt from other bikes, the compression is good. I am just guessing that it is rich although it idles unlike most 2 stroke mx bikes (from what ive heard). I am planning on taking the whole bike down to the frame in the next couple of weeks so I will probably just ride the piss out of it and hope for the best these next couple rides. I was mainly just wondering about the backfiring. Does it mean that the powervalve is staying open or something is seriously wrong or is it possible that the fuel from it being flooded ignites in the pipe before it starts. It only backfires when it is a bitch to start aka flooded. When I have it apart I will pop a new wiseco piston kit in it for sure. I will clean EVERYTHING when I have it apart and replace what needs replaced.