Piaggio Zip AC, lack of power

Hello all,

I rebuild my engine from 50cc to 70cc. New cylinder, new crankshaft and bearings. Removed the startermotor. The problem i face now is that there is no power at all.

The engine runs fine at idle but the acceleration is pretty weak and it only goes to 40km/h. The color of sparkplug is gray. I couldnt ride that much because of fine tuning everything.

I lowered the main jet from 100 to 90 because in beginning the engine was stuttering. That problem is now solved. I have already changed the sparkplug and the ignition coil. Piston etc. mounted correctly.

I still think there is some problems with the ignition. Maybe the stator coil isnt 100%. I m not sure.

What could be the problem?

My setup:
70cc Athena racing (0.6mm squish)
Athena racing exhaust
Polini CP 21 carburator (new)
Polini power fitler
Malossi overrange pulley (purple torque spring)
Malossi clutch (white springs)
Malossi winbell
Polini hi-speed variator (4.2 grams)
Polini evo 3 half pulley
NGK C4 race ignition coil