650SS running on 1 cylinder solved.

Success. We found the offending cylinder blowing back fuel out the carby instead of sucking it in. I decided it must have an inlet valve not closing properly. Ran a compression test and found 150psi v 100.
The head is now being checked over at a machine shop.

But I thought on your first post you said you had checked compression?

Quote

"I have checked tappet clearances, compression, spark. "

You have low compression now after a second check,?

johnm said:

But I thought on your first post you said you had checked compression?

Quote

"I have checked tappet clearances, compression, spark. "

You have low compression now after a second check,?

Click to expand...

Yes, bit not measured the compression. My bad.

Have you got the bike back together and running? I'd be interested in the result.