Many thanks to Clive who kindly posted me known working igniter unit. I’ve just put it on the bike and tried it but unfortunately it made no difference at all. The bike took ages to catch and run then ran like a bag of sh1t
he mentioned his bike was showing similar symptoms which turned out to be the cam timing which had jumped a tooth. I did check this earlier on when the problems first started but it looked ok to me? It also ran perfectly for a while which sort of rules that out but I’m clutching at straws now so I’ll check again. Any hints and suggestions welcome before I set fire to the bloody thing.
i've been waiting to hear the result of cranking over with the sparkplugs in and the battery voltage. if that is over 9 volts during cranking, I was going to suggest that the cam timing would be next on my list.
The fact that it won't fire on choke with the choke mod done and the ignition timing is checked and ok along with the spark being confirmed, it leads me to believe that the cam timing is off and that is causing low intake vacuum.
I've seen motors running fine and get shut off and the next day won't run and what happens is if the cam chain is loose enough, turning off the engine causes a drag force on the cam chain and the camshafts are still turning forward and the slack in the cam chain instead of being at or near the tensioner roller is now at the the exhaust cam and that's when the chain jumps a tooth, sometimes on just the exhaust cam and sometimes on both cams. Hyvo chains are a little more susceptible to this happening than roller chains.
So, yes check your valve timing.