The later models of the nsr dont make as much power from my experience and when restricted 15hp and deristricted only 24ish hp if they dont pull well up top so probly needs de restricting.

If u can find a alcast uk model or earlier still as they produce more power de-restricted.

On my nsr125 i dismantled the control for the valve removing all the electrics and cables and locked it in the open position, then i removed the restrictor plate from the intake and drilled the exhaust washer out.

With a few diffrerent carb changes, some material off the cylinder base, bigger jets and advancing the timing slightly i had a very quick bike that wasnt fantastic going slow ran and ran on avgas. (obviously not alot more work than described but basicaly what i did)

I would remove the restriction on you bike from the inlet manifold and/or the exhaust. if there are none or if **** still having problems then id swap the ignition control from a uk alcast model.

The rc valve is as andy said and is worth cleaning if u have the time and can be done with the engine in the frame.

Power loss could also be due to worn piston rings!!
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Honda nc23 CBR400 AERO 1986, 1990 honda NC23 Tri-Arm, 1987VFR400 NC24 Rothmans Rep, NSR250 MC16 1987, CL250s 1983. Moto guzzi zigolo 110cc 1958. Fantic 50cc 1972. Suzuki Cobra Race bike 500cc 2t 1975 , GP125 1975. Triumph T110 1954. BSA Thunderbird 1955. Ariel VB 600 1952, 1990 MuZ 125 etz.