Thanks everybody for the help
Last night I disasemble the other webra 1.20 I have and the cylinder exhaust ports look exactly the same.
I also will take other recommendations and what I am gonna do is to buy the cylinder sleeve and piston ring.
Since I hope the power will improve I'll switch to a 3 blade propeler.
Which one do you think will be the 3-blade equivalent for a 17x6 or 16x6 2-blade one?
As for the oil I use half castor half synthetic, but I guess it's been quite a long time since the engine was cleaned out
Regards
Omar