IMHO the fuels we get here in NZ are crap, and the fuel regulations have been written by the fuel industry so they can supply any old shit from any where in the world. The fuel barrons throw all the terminal flushings into 91 and the 95 can sit around for so long it is often out of specification by the time you get it, thats if it was to start with.
Pinking sounds like a hand full of marbles in an empty tin can being shaken very hard. I agree with Smokeu on this one, and thats a first. Pinking is preignition of the mixture under compression and is very very bad for a petrol motor. The octane rating is the ability of the fuel not to do this and is found by laboratory testing in test motors. Pinking is the sound of the burning fuel being compressed and the pressure and temperature reaching levels that are damaging your motor.
It amazes me how many people think octane and calorific value is the same thing. Octane is the fuels ability not to ignite under compression, thats all, however as the octane goes up the flame front speed of the fuel drops. Taken to the extreme if you run race gas in a low compression vintage motor the fuel burns too slow and is still burning as it leaves the cylinder and heats up the exhaust because of the radiant energy from the still burning fuel.
The calorific value of 91,95 and 98 is almost exactly the same, they are so close it is impossible to distinguish them from each other by any practical laboratory calorific method.
Some motors have a pinking sensor, my Harley hasa sensor in the rear (hotter) cylinder head that detects the ultrasonic noise of the preignition and backs off the ignition. I am not sure how many other bikes would have this but I doubt a 250 would.
I haven't ever noticed any difference between any of the fuels available here in any of my bikes, I just buy what ever is cheapest and use the money to wear out more tires.
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