These bikes have an advance mechanism?
I thought it was all pulse generators and sealed print circuits!!
I have been running with the air filter cover off but just put it back on today to see if that was the problem, so its been getting plenty of air.
Edit: hang on I do remember reassembling something similar to an old weights spring advancer, it's behind the pulse generators, damn I better check that out, I'd completely forgotten about such things, thanks Scunny.