compression test ok on both cylinders, valve timing spot on. Had BSD double check these for me. They came up with the same numbers as me.

thinking of shedding the 620 already!

Yellow, Delivered by a lorry, Have flashing lights for the hours of darkness, rhyms with Tip............

Trying to sell on the 620 already!

funny, i was thinking the same thing.

Yea mate, It was always the case that it will be prepped and raced but up for the right offer. I have done a load more on it the week, moto gp pipes the lot, does look good and sounds like rolling thunder.
There is a part of me that wants to do thunderbikes, I live by the rule that if i dont do it now i never will, Hasty, Probably but thats just the way i am.
Glyn

don't know anyone with a 583 motor kicking about do you.

I sold the one I had with my 583 to Kev Mooney so he has one but i feel pretty certain he wants to keep hold of that, I will keep my ear to the ground for you though m8
Glyn

Andy what have you changed I take it you have changed the coil, the CDI unit, spark plugs, I know you say its sparking but a break in a HT wire or plug itself would still give a spark but may cause problems under load.

As suggested a compression check is needed in case valves aren't seating

I think you have to change one thing at a time now, starting with swapping the plugs from front to rear, to prove that each pair of items will work on the rear cylinder - even a new plug can be duff.
You havnt mentioned the carbs - have they been apart ?
If so, are both the diaphragms working properly (you can test by hand by carefully pushing them against the springs) cos that may well stop one starting (!)
Have you flushed the float bowls to make sure its not water making the plug wet ?
If you flushed the float bowls was there any muck - cos that might have blocked the pilot jets.
Have you tried a squirt of special starting-juice (cant remember what its called) into the front when the back is turning the engine over ?

time for bed now
good luck
phil
btw - where are you in case someone wants to come round ?