ORIGINAL: niche

Hi all
I have two webra 1.20 speed, running with same fuel, glow plug, pump, tank, etc
I am very happy with one I can run a 17x6 with no problem but with the other one I have not able to run even 15x8.
For the one I have problems with I have set the idle properly , when tunning the needle at full throttle it feels like is never reaching the highest rpm possible.
Once I start closing needle to increase RPM there's a point when it feels the engine too lean and then I have to reopen the needle but I never get the felling it's runnig at highest RPM, you know what I mean.
I am running a 15x6, but as said above with the other engine I run 17x6 with no problems.
I inspected the engine i have problems with and noticed the piston ring (in the top) was "welded" to the piston, (maybe the person who broke-in this engine did not do it properly and overheated), I loosened it, remove the carbon in the top of the piston, and now I measure the compression for both engines and the one with less lower power gives more compression with the one I am fine with.
Now I am lost, I was thinking about replacing the whole cylinder-piston-ring set for the engine but I am not sure it's gonna help me.(since compression is fine).
I am not very wise on webra engines, I know the compression I read has nothing to do with the one when the engines is warm, but anyway I want to know what to do.
I would really appreciate any help you guys can provide me with, it's ons of the first time I feel lost and not knowing what to do.
Regards
Omar