Thanks Garyc660r, first thing I do before pulling the carb off is check the compression in the cylinder, the dealer says it should be 170 +/- 10. If the compression is to low what should then be done? If the compression is fine then I will pull of the carb. and see what I can find out. Any more suggestions would greatly be appreciated. FYI I posted this same message on 3 other dirtbike boards and have yet to have a response.

99 Banshee, FMF Fatty's, Power Core 2's, K&N filter with precharger, yellow maier racing plastic

99 YZ125

 

Compression to low =
Check for leaks
check reeds for no cracks and proper operation (this seals the combustion process).
next, I would have the cylinder inspected and replaced/bored if NECESSARY (meaning get someone qualified to look at the bike before spending a bunch of cash)...if this needs to be done, get new piston/rings/gaskets too.
If compression is good, the carb could be the culprit.
Anyways, this is what I would do...if you don't know how do check the carb/copression/etc., get someone to look at the bike that's qualified to check it out...you don't wanna make more trouble than you already have. Good luck.

 

If the compression is too low, then put a Wiseco Pro-Lite Top End kit in it. They are good pistons, and come with piston, rings, and wristpin. You will also need a gasket kit. It is borable, but you have to have it re-plated. Not that expensive.

My Rm125 ran exactly as you mentioned before I fixed the jetting.

 

It can be flooded!!!! Run 50:1 premix. It will run much better. It's the first place I ever see people premixing as much!! I had never heard of going richer than 50:1, and some of you guys talk about 32:1 as good thing.
A YZ runs 50:1, give it a little throttle when kickstarting...should be correct.

 

does anyone else have any thoughts on what the problem could be? I'm taking it all apart tonight and checking it out. Anymore thoughts would be greatly appreciated.

 

My old two stroke yamaha 125 3 wheeler does the same thing and it almost out of compression. You ought to call a little motorcycle repair shop they can probably tell you a quick way to check to see if it has enough compression. Hope this helps.

 

Well I took the carb. off lastnight and checked it out real good. Still has stock main, and pilot jet and the needle was set on the stock 4th clip. I leaned the needle out a little and moved it to the 3rd clip...cleaned the carb real good and put it back in. Tried to start it and it was doing the same thing. Start for a second and then foul the plug. I pulled the plug off cleaned it and put it back on the cap. I did a spark test...but was getting a real weak blue spark. I am going to buy a new plug today and try the spark test again to see if it was just the plug or an electrical problem. Has anyone else had this problem. Should a check something in particular?