ec 300 2005 won't rev high nor idle...

[hannesd]

a friend's got an ec 300 that has had nearly everything checked but still doesn't run well.
it doesn't idle, and doesn't rev past halfway.
starts fine when cold (even without chocke) but when warmed up it sounds like it's VERY rich as if chocke was on all the time, this is how i can discribe it the best.

engine has even been split and put new seals on the cranck, new (carbon) reeds.
we swapped out my carb from my ec 200 and still doesn't run well, but somewhat better since it's a bit leaner.
silencer has been removed to check if it wasn't blocked, to no avail.
PV moves as it should.
CDI has had an update from gasgasdealer.
funny thing is, that the engine runs much smoother when we open the drain hole at the bottom of the engine i guess it then runs better as it can't suck that much fuel in...
only thing left to swap are the ignition coil and static timing on the 2K3 ign.

anybody have an explanation on how it can run better without the drain bolt??

thanks for any input.

Hannes.