Motorcycle Repair: 79 cb650 carb problems, speed jets, lean mixture

Question
Hello!
I have been trying to bring a 79 cb650 back to life and its working for the most part, but the carb seems to be acting up. The engine fires up and revs fine, but sometimes there is backfire through the carbs and sometimes through the exhaust. There is also a flat spot in the throttle, where when you rev the engine, it stalls and dies if you hold the throttle constant at that point (around 3000-4000 RPMs). If you ease off and rev it again, it comes out of the stall. The one thing that i made a note of is that I took the float off the carbs to clean it up a bit and some of the screws were stripped and do not torque up anymore. I also noticed that when adjusting the choke, the butterfly valves do move, however the engine stays at the same idle speed. Is this indicative of a valve leak? (perhaps because the screws are not torued?)
Any insight would be appreciated!
Thanks!
-Andrew

Answer
No, it sounds like carburation to me. The flat spot is a lean mixture that can cause the backfiring you hear.  I think if you applied a little choke when it acts up you'd find it comes out of it and runs better.  You need to make sure the low speed jets are not partially plugged and that the float levels are correct and that should take care if the problem.

Regards
Rich