Misfire

I have just bought a 650S 1999 30000mls it has a Quill can not sure if its been rejetted? It appeared to run very well until I took it up to around 110mph it started misfiring, I pulled into a carpark for about two hours. When I started it up it was still misfiring after a while it seemed to be ok but I never done over 60mph. After a day or two I went out for a local ride & reved all the way up past 9000 revs it started misfiring again and cut out, after a few minutes it started on one cylinder before eventually running ok. On Sunday I went to a mates after telling him the problems! He check the fuel tap & on from there was a vacuum box of some sort? inside the diaphragm looked ok but there looked like two round valves one of which looked out of shape! my mate seemed to think they were not important! so took them both out. He check the jets in the carb, everything looked fine. It seems the cylinder giving the trouble is the rear one! I did wonder if it could be a ht lead? Any clues would be greatly received.
thanks Don.

It could be a loose coil connection, something I had an issue with 3 yrs ago, check there are no loose connections and it may solve it, but I'm not promising anything.

Does it do the same thing at the same revs in all the gears, or just in top when going for max speed?

[dizzyblonde]

like Tim says a coil could be the answer. I have jut replaced the rear one on my yellow curvy, as when riding across the works carpark it would misfire, cutout or just play silly games. We replaced the HT lead first, which was foobarred anyway, but i had a kind of shorting noise as well.....replaced the coil and the silly behaviour has stopped. Still haven't got to the bottom of starting on one cylinder though

[embee]

Sounds like your "mate" just gutted the fuel pump for you.

I have a Quill T3 and it doesn't need re-jetting, stock carbs do fine.

Sounds like a general good going over is called for. Like most of these things you can't just diagnose it as being any one item. You need to work through it and make sure everything is correct and serviceable.

As the others say, however, coils are a good candidate along with other components of the ignition system. You also need to thoroughly check out the carbs, chokes returning properly, water in the tank etc etc.

Thanks for all the comments, I shall check out some of the connectors tomorrow!
Thanks Don.