He was out on it today, running fine, switched it off and it wouldn't restart. Spark is fine, I checked it by grounding it on the head and turning it over.

Leaving it overnight to dry out in case its flooded. I'll see what happens tomorrow.

Check the carb too. Mine kept getting a dirty carb (blocked jet), so I had to fit an extra inline fuel filter...
It started but needed the choke to run...

There are all sorts of things. Is the compression the same as always?? These things can run on one ring. Try a new spark plug as the spark might not be sufficient, then its down to a complete clean of the carb. Try leaving it over night with the spark plug out cos it might just be flooded. Try a bump start aswell. ALso check how clean the reed valves are.

it will be electronic so timing adjusts itself.they have a little black box under the seat normally.you can move the stater plate slightly but won't make much difference to the timing.has he tried adjusting the air mixture screw on the carb???

or there is a mixture screw?

chain?

A mate has an RM80, its getting spark, fuel is OK, compression is OK, I'm thinking timing - how is this done on these?