I have a 1993 327cc gas gas everything has been running fine untill yesterday when it seemed to backfire and now I can't start it, I've checked the sparkplug and theres no spark, I'm a bit of a newcomer to trials bikes so please help where do you start to check.

thanks, Barry UK

Barry,

You may want to check these things:

1) Try a new sparkplug gapped to .020".

2) disconnect the kill switch, it may have shorted out and needs to be replaced.

3) make sure all the connections are clean and tight in the electrical system and put some dielectric tune-up grease (you can get this in auto supply stores, it's used in sparkplug wires) in the connectors before snapping them together.

4) Check the sparkplug cap and replace if necessary.

5) Have the electrical system checked out with a meter to see if the components have the correct values.

6) Go over all the wiring to see if any wires are shorting out. It's common for the wiring insulation on older bikes to have rubbed through if the wires are not secured well.

Give these a try and let me know if you need more help. Jon

(NOTE FROM JIM SNELL. The flywheel key is sheared...)

Absolutely, and obvious when Jim points it out. It's not uncommon for some
of the older bikes to have the Morse Taper damaged because the rider thought the key is what's holding the flywheel in assembled alignment rather than the .001" interference fit of the flywheel hub and crankshaft. They shear a key and don't fix the damaged taper when replacing the key, which sets it for failure in the future. This is one of the many reasons why I like to have Jim review my answers.