Power loss caused by bad pick up coil?

Would assure that all valve clearances are within specs, as loss of power may result from a too tight valve.

Failure of a valve to fully seal when closed may also result from a burned or cracked valve, or a damaged valve seat, or a broken valve spring.

Good Fortune!

Tnx guys, i have a little update in the problem story: i removed the clutch and it was fine so I installed again, then I removed the carburetor and I did wash it, then put it again and proved the bike, but the problem was still. A little sad and tired I forgot the bike for a couple of days, but yesterday I had to go to hardware store and decided to go riding the bike again,so without trying anithing since the last failed test I sterted the bike and amazingly it runed as good as it used to do , no problem at all, I have not used after that 5 kilometer ride but this makes me think a couple things:
*Can`t be an engine problem or it wont return to work finel so suddenly by itself….. right?
*It should be somthing electrical like apbling suggest an that´s why it works fine some times and some times not without an eviten cause .
I´ll test the bike tomorrow again to see if it still works fine or it is failing again with the same sympthom.
Some new ideas meanwhile guys?