2004 GSX-R750 Gas??

Question

Hi, I was wondering if this bike having about a 12.3:1 compression ratio can run 89 or maybe even 87 octane gas smoothly

Answer 1

Probably not.

Answer 2

It may run poorly and probably use a lot more gas than if you run it on premium.

I have a V strom 650 (injected modern V-twin) which uses a lot less fuel on premium, more than making up for the price difference. This is because the engine management runs it leaner on better fuel. Your gixxer should be the same or more so because of the high compression.