It appears the old coil was a bit past it. The 'proper' coils are over a hundred quid so I'd convinced myself that the old one was OK as I was getting a spark when trying it with the plug on the block. It would always start but by fuck it was a trial sometimes. My brother [1] kept muttering that a spark might act differently under compression before wandering back to his 4x4 monsters. I bought a cheap [2] coil on ebay, made some brackets for it and gave it a go. Huge improvement immediately. Much happiness! The new carb' wasn't a complete waste of money. It seems to settle to a nice tick over much sooner now and the choke can be used as intended. The silencer is blowing like a train all along the top seam and I think I'll take the bugger off and weld it up before the spring. It's a lot of fun to ride about on though. Low seat, wide bars and scary car scratching attitude :D Oh and a nice new set of Trelleborgs. 1. A repairer of cars and things. 2. Twenty quid.