HI, I'm new to the world of NSR's (and 2strokes come to that!).

I've just purchased an MC21, a bit tatty (has anyone a top fairing spare?), but run's well and the frame etc is straight.

After an initial check over, new plug's (had B8ea fitted!!!), new chain,front tyre and rear wheel bearing's, everything else seem's fine.

Little else is known about the bike or if anyone has attempted to tune the motor.
Twin carbon end pipes both exit on the right of the bike, (make unknown).

A compression check showed both cylinder's to be about 140psi.

My first "proper" ride was a love / hate affair.

The bike run's sweet through the low midrange (upto about 6K), but from 6500rpm to 8500rpm the motor feel's strangled, flat, not misfiring but a kind of 'stutter'. This characteristic is worse in higher gear's and/or going uphill ie under greater engine load.

As soon as the powervalve move's at 8500rpm the exhaust note change's and the bike takes off instantly and again rev's cleanly and smoothly upto (and into - oop's) the red line.

I believe the valve should switch at about 6500rpm, is this right?

Does anyone have any advice / opinion's on what might be wrong?

My first port of call will be to check the powervalve cable's adjustment.

I will then check to see if the bike has been derestricted. (there's no black box)

Is there anyway to reduce (or check) the rpm at which the valve alter's, as this appear's to be the problem, would a late opening valve cause this type of running alone?


Any help much appreciated!

regard's Phil

N. York's

'01 TRX 850
'76 400/4
'93 NSR 250 MC21