Seems to have been used by a few people to good effect: http://www.mightyram50.net/vbulletin/showthread.php/2642-How-to-Soften-Old-Hard-Rubber I'm also thinking it's unlikely to be the cause right now, but given how clean I believe the carbys are I'm really running out of ideas. New plugs could be gapped wrong but not sure that'd require a tonne of extra fuel from the carbys? Once I got them apart last night I spent a decent amount of time trying to get my bench sync as close as I possibly could, with some luck that'll help. Guess we'll find out tonight depending on how fast I can get it all back together. Don't really want to be firing it up much past 9pm because they're sure not quiet 250s I'm pretty sure my wife will be happy for me to buy a heat gun if it stops me stealing her hair dryer.