Loosing power at 3/4 to full throttle after 70cc kit install

[tempbond]

Hello !
I added a Polini sport 70cc cylinder kit to my 2 stroke scooter and besides taking out the variator ring, everything else is stock. I did buy a main jet kit and an idle jet kit for tuning and a derestricted CDI, but haven't installed any of that yet, as I wanted to test the change with the 70cc kit on its own to limit the variables if something went wrong…and something did go wrong 😩.

The engine starts normally and for the little I've tried it, it seems to have more power, but I can only open the throttle to about 2/3 or 3/4 before the engine looses almost all power and seems like it will die. When that happens, if I release the throttle a bit, the engine goes back to normal.

Edit : forgot to say that I ajusted the spark plug gap to .65 as it was .20 stock (NGK BPR7HS) and owners manual says it has to be .60 to .70 (but engine ran fine at .20 with original 50cc cylinder)

I've read somewhere that this happened to someone else, but I haven't been able to find that thread ☹️

Does anyone know what's going on and what I have to do to fix it ? Thank you !

PS : if it helps, it's a TGB Express 50, Mikuni carburetor, stock main jet #60, stock idle jet #17.5

[aeroxbud]

You need to put a bigger main jet in. You are probably running dangerously lean.