Motorcycle Repair: Misfire GSXR1100W, honda cb250, air leaks

Question
I have a 1995 GSXR1100 and have a problem with the running of the engine. Let me start at the beginning. 1: 164km per 16-17Litre of fuel, had the carbs overhauled (cost a fortune) now getting 260km per 15 litres. 2: It ran OK for a week after carb work, but now has a misfire/flatspots at idle to around 3500RPM - 4500 RPM (sounds like 2 cylinder at idle, Honda CB250) and feels like it wants to backfire when changing down under load. When you twist the wrist and the good gauge is heading passed 4500RPM and at 100km/h plus it is turns back into a GSXR1100. what the #@*$ is going? 3. I am an australian, so leave the spelling alone!!!

Answer
Rick,
Midrange flat spots have been a problem for some GSXR's.
Possible causes are vacuum or intake air leaks,
midrange lean fuel, Fuel and/or idle jets/tubes recontaminated by tank rust.
Carbs way out of sync, bad spark plug(s)
Tight valve clearance. No exhaust backpressure. Exhaust header leak.
Poor ignition advance.

Do a run at the problem throttle opening and read the plugs,
black is rich, white is lean. Try new plugs,
Check for any intake, emission or vacuum hose leaks, raise the carb needles
to richen mid-range fuel mixture.
Were the carbs synchronized after the overhaul?
Check cylinder compression.