The [integrated] centre crank seal on the 89-96 models is a known NSR250R weak point, and even more so with fuels containing ethanol. If you can get pump fuel without ethanol, we advise you to use it, whatever the cost! Failing that, use the fuel with the least ethanol content you can find.
Not only does the centre seal appear to deteriorate significantly fast when using ethanol content fuels, the ethanol can also be highly incompatible with many of the fuel system components from the 80s & 90s bikes.
We have often found that when setting up bikes for modern fuels, we've needed to increase the pilot jet size slightly. This can improve both starting and slow speed running.
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Andy.
NSR-WORLD.COM
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