need some help tuning a new engine

[Moe]

hey all,
I've just got my new OS 28xz. just finished running it in and i was being patient with it too. dont wanna spoil my first expensive engine.

anyway... after breaking in was completed i started tuning the engine. problem is, every time the tank is full, it seems to run rich. once it reach to about half a tank or lower it becomes quite lean.

is this normal? i didn't notice this behavior when i was using the 454 losi RTR engine.

car: Losi 8T 2.0
engine: OS MAX .28XZ
pipe: OS T2060SC
Plug: OS P7 medium
fuel: Sidewinder 30%

had to add another head shim to reduce the compression cause it was running really hot (0.2+0.1+0.1mm shims)

any opinion???

thanks