EC250 SM stuttering + fouling plugs

[gasser250sm]

HI, im new to this forum and gassers ! I bought a 2002 gas gas EC250 supermoto and i love it ! its goes like F*** but thats only after its cleared itself out and you got to thrash it everywhere (which is a bad and a good thing) i do use the bike on the road mostly. Ive tried almost everything mechanically to fix it. The problem is if you go slow for too long then go to give it some, at midrange it stutters and splutters for a few gears to about 3rd then it comes into life and nearly flips you of the back it does sound 4 strokey which could suggest jetting but i have tried jetting makes no difference to the problem just makes it slower/quicker top end. also if you go slow for too long and dont give it some itl get very smokey and about to foul a plug i then have to thrash it to clear it out, atm i have to use a 3 point audi spark plug 6 grade as it lasts a lot longer than the br8es br8eg b8es br8eix, and does not foul as easily. It also blows rear bulbs, i dont know anything about electrics but i feel the spark isnt strong enough or CDI or something This is what ive done so far:

Replaced Right hand side crank case seal
Replaced left hand side crank case seal
Replaced rubber inlet manifold
Brand new Boysten Power series reeds
New air filter
Running 38 pilot jet with a 178 main ( in the UK)
Cleaned and service powervalve, it is running correctly now
Replaced head o rings and base gasket to eliminate the problem of water seeping through
Brand new rear DEP silencer (as other one blew to pieces)
New reed block gasket
New exhaust gasket and o rings

I did all this without making a difference but recently i changed the left hand side crank seal and the rubber inlet, and after wards it would not start just backfire, (i thought could of put stator in worng place, but it was exactly how it was before ) i then managed to bump it and it was really struggling couldnt go more than 10MPH i then found my reeds where non exsistent i changed these and it started fine and had very good low end power without stutter but no top end as if the power valve wasnt opening, i then took top end of and powervalve apart and it was really coked up i cleaned it all put it toghether and its doing the same thing backfiring !! so its gone from runing crap to not wanting to start and going slow, this leads me to electircs ? please help

Thanks for the help in advanced.
Dhyllan