my 2 stroke yz 125 is broke!?

Question

i was riding in 5th gear all out and the bike turned off and the back wheel locked up.i tried starting it back up i did about 50 kicks and stoped 4 a minute i tried to kick it again and it was stuck like it would only go down half way and its still like this after 2wks so idk whats wrong with it but go on youtube and i have a video showing this problem...heres the link ................. http://www.youtube.com/watch?v=jpDcFGdXhZY ......k thanks guys

Answer 1

You are done. Your engine has seized. You need to do the engine that means open up the stuff replace the piston ring if it is minor or rebore the cylinder and fit oversized pistons if it is major. In any case it would be expensive.
What happened - You probably were not using enough lubricant (2T oil) with your fuel. In a 2 stroke engine, the 2T oil works as a lubricant working between the piston rings and the cylinder wall reducing the friction and keeping the temperatures down. When you drive all out and there isn't enough 2T the engine temperature increases to extreme levels and the piston ring melts and fuses with the cylinder wall, immobilizing the engine which caused the wheel to lock. First time it probably didn't fuse so strong and you were able to kick. Since the engine was already superheated, each kick (of the 50 odd you did) infact heated it up further and finally the piston ring fused strongly with the cylinder. This has resulted in the unmoveable kick starter.
If you have a separate 2T tank and there was enough 2T, it must have been the 2T pump which failed or was not tuned correctly (not providing enough oil). If you mix 2T directly to your fuel, then the mix must have been incorrect.
I would say you are extremely lucky not to have injured yourself badly. At high speeds (40 mph+) a wheel lock on a small and light bike has the potential to be fatal.
If this heppens in future - Never try to start the bike immediately, wait for at least 30 minutes and then try to kick back. If it starts go to the nearest fuel station and add some extra 2T in the fuel (assuming you are not carrying any). But this will ofcourse cause the bike to emit a lot of white smoke. Next go to the nearest mechanic to assess the damage and get the root cause (2T pump/ inadequate 2T mix) fixed.

Answer 2

It could be very an oil related issue. It could be the wrong ratio or incorrect oil.

Have you been inside the Mikuni Carburetor? There are many tuning areas where obstructions occur. The pilot jet may have been obstructed or a too small pilot and main jet may be in it. Did you change the slide valve to one wider opening? Did you lower the main jet needle? All the above can lean out the total fuel mixture which causes excess heat. Almost always a burned piston and a scored cylinder wall will result. When you re-do your cylinder shoot for the next larger piston size. Occasionally they come in an .005 or .010 over size.

Have the cylinder honed on a Sunnen honing machine to clean up such a small amount of cylinder damage. Find out from the piston and ring manufactor the optimum cylinder wall finish. This will aid the ring or rings to seat fast and properly.

Answer 3

oh the 250r would smoke that YZ-125 all day, i know this because i have a CRF250R, and 2 of my friends have 125s' one has the CR and one the YZ and I would smoke them all day long, and the YZ is maxed out on parts and so is the CR. And at he time all i had was dual carbon fiber pipes, they will be crying after it's over, keep your RPM's high, and and shift late, but shift before when you hear the rev limiter, HOPE THIS HELPS..

Answer 4

time to get a rebuild good luck