Please can anyone help? My mc18 starts fine cold and after a few seconds revs at 5/6 000 rpm without touching the throttle, turn of the choke and after 30 seconds it drops to 2000 and then a minute after it will drop to 1100 and idle perfectly,yesterday out on a run cruising along @ 70 mph fine,then i gave it a blast it flew straight up to 10000 rpm in top then all of a sudden it lost power surging like fuel starvation,i slowed back down without choice to 60 mph then after a short time wound it back up and it shot back up to 10000 in top pulling very strong and as soon as you close the throttle off a little it starts losing power and surges again, when stationary if you hold the throttle @ 5000 rpm it will rise up to 6000 rpm without moving the throttle,Lesviffer and i reset float levels and cleaned carbs throughly,started it today and its the same,any comments or advice greatly appreciated, jonmac
_________________
John

is the filter in the fuel tap is blocked??? did you try cleaning the seat for the float valve with brasso on a q-tip in a cordless drill??
if your thinking of replacing the fuel filter , it just as cheap to buy a new fuel tap (comes with a filter).
also check the breather in the fuel tank.

Sounds very much like an air leak - the motorssurge in revs when the mixture goes lean - which of course could also be fuel starvation as mentioned above.

Check all of your rubber seals are properly fitted and in good condition, including the carb to case manifold.
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Have you checked carb balance? I had the same problem with mine once and stephenRC45 told me to check carb balance so i did and it sorted it.