OK Guys, thanks for all the input. Firstly I must check the choke slide as Wombat says, then obtain or make a tapered gasket/spacer, tuning is not possible until I can get it to run properly on both cyl's., the battery is brand new and fully charged showing 12.7 volts so I don't think that's the problem, broken valve spring could be it though but wouldn't that give me a reduced compression? I will re check the valve clearances though when checking the springs. Having a wasted spark means it fires the same cylinder from the same Boyer coil on the stator so having swapped the leads should have eliminated caps, leads and coils. (Same as turning the stator plate 180 degrees?) The only other thing I have done is swap the mag twice, the first time it turned out to be caused by loose points!!! the second time was due to not being able to see a spark on the left hand new plug which turned out, when I had the mag on the bench, to be sparking but right up inside the body of the plug. I used a drill to drive it. Which leads me to believe the fouled plug was caused by the same problem I have now. The first time I had it on the road it started missing under load up hill and finally carked it and had to get my son to fetch the trailer. The second and last time it went well for about 6 or 7 miles and then started to miss again just after leaving an 80 zone and in a 50 zone, so limped it home and fitted the Boyer. Both times it was well warmed up but had not been over stressed. I could have had this problem right from the start as its hard to pick up on until removing the right hand plug lead. The misfiring could be because there is not enough combustion to keep the plug clean. Oh yes...sorry I meant 928 carb' which is same size as the inlet. The other thing that worries me is that when I machined the housing for the Boyer rotor and stator, I made a mistake and machined the housing out a bit too much allowing the stator to foul the magnets on the rotor so had to realign the stator by feel which means the magnets could be passing the coil post on one side closer than the other!! WHY DIDN'T I TAKE UP GOLF OR MUSIC!!! Cheers and thanks again guys. Will keep you up to date as and when things hit me in the face. Gerry