there are pipes going to the carb and elseware on the nsr's so check on the carb that they are conected and that theres no holes in them, are all the screws on the pump torqued? if its petrol check the pipe maybe theres dirt in the carb float bowl keeping the float needle open drain half a litre thru each if it looks like it could be if not strip the carbs and clean them dont disturb the settings if possible tho.
hope this helps
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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.