Correct

Being that the GZ250 only has a compression ratio of 9:1 there is absolutely no need to run anything higher than 87 octane. Running anything higher than that will likely result in less power. Octane is resistance to detonation (knock) and it actually packs less power than 87 octane (which is actually a more volatile fuel) . Higher octane fuels are for higher performance engines with higher compression ratios and or forced induction.

Not to resurrect an old thread, but I was going through an old GZ250 manual for another reason and saw where the manual recommended using 91 octane gas. I will have to check and see if the manual for my '09' shows the same thing.

Bottom line, I tried high octane fuel in my GZ for a short time and it ran really doggy and with a lot less power. Just a quick FYI. Ride safe.