Hi,

Just given the above a major service - new plug, valve clearances etc. At the same time removed an IMS tank and put a rubber pipe from the now defunct vacuum take-off and plugged the other end with a bolt.

However, the bike now starts but backfires when idling and when I close the throttle. It didn't before.

Any suggestions?

Cheers,

Scoobie

sounds like a vacuum leak.

If that's all you did, then it's probably something you changed or did.

you can use the smoke test to see if you have a vacuum leak at one of those connections. I always have to borrow a cigarette, as I don't smoke, but it works pretty good. You'll see the smoke get sucked in the vacuum leak when you find it.
-T

or carb cleaner sprayed around the area will cause the revs to rise if it enters the intake.
Gotta think on this one a little more though as my bike is apart right now and has to be back together tonight to race tommorrow, better hit the garage, good luck.