Can anyone help me with a fuel problem?

I need an experts opinion...

I'm having trouble with the fuel system on my bike. The bike starts and idles fine. As i take off the bike runs good but a about half to full throttle it feels like it is starved of petrol or there is air coming in, it splutters and the revs die then pick up then die and in some instances the bike stalls.

The bizarre thing is when i ran it in it all worked perfect?

This is what I've check so far.

I have removed the fuel filter from the tank to aid the fuel flow, and it has been replaced with one in the fuel line to the carby.
I have checked the filter fuel direction and it runs i the correct way.
There are no kinks in the hose
The hose dose not run higher tan the filter.
The fuel mixture is correct. 40:1
The float level is correct. 16.5mm
Cleaned jet, atomizer, starter jet and bowl
Tried a larger jet 98
Adjusted the clip hight down to the third notch.
New gaskets and used silicon the seal them.
Mixture screw is 4 and a half turns out so it will run rich,

carburettor:
Dellorto PHBG 21mm black edition
Main jet: 92,
pilot jet: 50,
needle W7, clip is set at the second notch.

engine:
SQ 39cc 3 port, water-cooled, polini reverse replica
the engine has only been used 4 times and two sessions were to run it in..
Polini carbon reeds and cage.


can anyone help?

are you still using the rep coil or plug? the rep gp3 coils are notoriously bad. check all the wiring (theres a fair bit of it for a simple circuit for some reason) and worst case get the polini coil box as a precaution. and obviously run a decent plug in it but ill assume youve got one from the other things youve tried

thats all i can think of. whats the plug look like after a plug chop at 3/4 or WOT. if it looks good then id imagine its the coils gone bad.

oh and maybe try it without the fuel tank cap on. sometimes the chinky ones dont vent proper and cause a vacuum in the tank = no fuel flow.

good luck hunting down the prob anyway

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my gp3 rep had the same issues and the coil box was loose causing it to miss and fart and feel like a fuel problem.
tightened her up and it was mint as

thanks boys,
for the leads on the problem, i have replaced the original coil with a polini one but, ill need to try out the ones you sent me glen with the engines, see if they work better. a new plugon its way.