Nilo,
No, you're fine in that department, the needle he is talking about is the "remote" one, the highspeed needle. A squared off low speed screw is fairly normal. In your case, I highly recommend you find someone near you who has good running engines and get them to help you. It's hard to troubleshoot engine problems on foums like this.

Juice,
If the engine ran fine, then started going rich, something changed to cause it, and the question becomes "what changed". Did you switch to a new brand of plug or fuel etc? Different fuel tank or plane? new prop? anything.

If you take the limiters off, you should be able to adjust the low and high speed settings more to the lean side, enough to get the engine to go past peak and not run well. Start up the engine, and go to full power, then lean the engine out until it goes past peak rpm and slows down. Then back it back out and set normally. This will tell you if the high speed needle is working or not. If you get all the way to the stop, and it still is running rich, then Jetts is likely right, something is holding the needle open. If the high speed can be adjusted from too right to too lean, do the same thing at idle, using the low speed screw. You can turn that quite a ways in before it stops turning. If you moved it all way in, and still the engine is rich, something is really off in your carb. Depending on the carb design, I can think of a few possiblities, but I don't want to go in to them, as I don't recall the Evo's carb well enough to say which apply to that carb and which don't.