Someone knows of algun tutorial to modify an engine weed eater in order that it has mas power?

Plenty of guys on here have played with all types of weedy motors in the past and a few of us are still having fun with them!
If you can tell us what motor you are starting with, more than likely we can point you in the right direction.
It is all too easy to go backwards with your mods if you are inexperianced then have to go looking for another motor!
Better still post up some photos of your engine as there are multiple engine types when it comes to several of the brands even in the same cc class!

Chad.

If you don't have time to figure out port time area, you may be able to cheat a bit, and copy the port time area (height from TDC, and width of all ports, and corner rads) of the stock RC engine, if the stroke is same and you don't break through the casting. Pipe it with a proven RC pipe for stock RC engines, May be advance your ignition time a bit to match the stock RC ignition time, add a 12.7mm carb and easily double (or possibly triple) your utility weed wacker engine, and still keep a good useable range of power. After all that work, you might have found a better way with a stock Zen G260. It is hard to get a utility engine to work better than a stock G260--but fun trying.