Gx200 mod skip at 6600rpm

[Yannick]

Hi
I have gx200 kart.
Cam 285
Flat piston forged and long rod wisco
Roller 1.2
Big valve
Head 22cc port and milled to 0.070
S2 flywheel
Mikuni 24mm carb jet 140 pilot 20
Spring 37 lbs
Pushrods moly 5.5
That's what I have .. The engine start skip between 6500 and 7000 rpm
I don't know why ... Do you have any suggestion ??
I try my oem carb port and do the same thing
Thank for your help
I want go to 8000rpm
Sometime when I cranck I have back fire in carb

 

[joler1302]

Cam dots lined up?

 

[jsstump#70]

First things that come to mind are coil, plug suppressor, timing, coil gap, spark plug. Is intake valve sealing ?

I too would consider coil. Get a Honda coil and put a good quality nonresister boot on it. Very well could be a fuel issue also. I am not familiar enough with this carb to comment about jet selection. How does the plug look?