I have a problem with my morini (...as usual...

the engine does not revs up...
the engine is very fast, sounds good, have good start when cold/hot,and kilometers per luter of gas are more or less always the same...
but tryng to rev the engine over 6.000rmp is impossible...
the engine simply won't go over... looks like some sort of rev limiter...
the rpm simply stop to increase when reached 6.000
neutral or gear engaged (driving on street) makes no difference...
the alternator impedance measures around 220ohm, it is in good condition
swapped the coils and pick-up with brand new one from deltaprogetti (170 euros)
swapped three different magnet
cleaned carburettors two times and all jets and carb holes with diluent and compressed air but nothing...
timing is good
basically everything works pretty good! but i can't rev over 6.000rpm






what happened?
what to look
what to look again?
guys help me, i love my 501 and i hate to drive it in those condition


many many thanks in advance from italy
