Motorcycle Repair: Locking Tire, valve seals, yamaha 125

Question
Hi Chris, I have a problem with my Yamaha 125 dirtbike. It's a 1981 which generally runs great, but last time I had it out, I did something to it. First off let me tell you about how I start it. The kickstart does not work any more so I run start it. Anyway, when I run and jump on it, then hit it down into 1st gear, the tire locks up and it dosent start or even try to start, it just locks up and skids. I thought it had something to do with the carb sticking, but I took that apart and cleaned it so it works good now. If you could help me with this and hopefully tell me I didin't blow the engine again it I would be very thankfull.


Thanks, Chris


Answer
Hi Chris.
 When you have the bike in gear, can you turn the wheel at all?  If not, then the problem is not the carb, it is the transmission.  This could be related to your non-functioning kickstarter.

If it turns but will not fire, then the problem could be in the carb, the electrical, or in the cylinder and/or head.

Any problem with the transmission like you are describing requires removal and disassembly of the crankcase.

If the problem is that the engine will turn but won't fire, then start looking for shorts and bad components in the ignition system.  Check everywhere between power and spark plug for shorts, grounding out and arcing as well as components that are not withing specs.  You will need the repair manual for those specs.

If the problem is in the cylinders, then you are looking at shot pistons or worn rings.

If the problem is in the head, then you are looking at a valve adjustment, bad valves or bad valve seals?

Check those out.
Good luck.
FALCON