Motorcycle Repair: 81 Yamaha 650 Special II, yamaha 650, valve timing

Question
Falcon,

I have a 81 Yamaha 650 Special II, I've been starting it about 1 or week or so through the winter just to keep it ready.

Now it wont start, cranks over fine, gets gas, when I turn the key off... it back fires?

What causes that?  How can I fix it...

Thanks,

Michael

Answer
Hi Michael.

When was the valve timing due?  Is it overdue?

Have you checked for shorts in the ignition system or for a bad ignition fuse (check that fuse with a meter, not just visually)?

Backfiring is, most often a product of valve and ignition timing.  If the ignition timing is off, then it will backfire, but if the valve gap is off from the timing, then a backfire can occur due to what is called compression fire.  That occurs when there is enough fuel and compression to ignite the fuel in a cylinder.  Not enough to run the engine, but it will give you a dramatic effect.

Start with the valves and the ignition circuit.  My guess is that your problem is there in one of those.

Let me know what happens.

Good luck and ride safe.
FALCON