What Octane of Gas Should I Run

[coolhuh]

I recently bought a 1988 250R, the owner used half 110 octane and half 91 octane gas. He does not know the compression of the piston or the dome cc's on the cool head. I checked the compression and it was 165lbs. What octane would be safe to use?
Thanks

[Tom TRX250R]

91 Pump gas should work great, running anything over that and you are pissing your money away!!!

[beerock]

if you did the compression right then that motor is due for a new top end if it has a high compression dome. new piston ,rings, wrist pin bearing, Bore and Hone.

then do a compression test.

what year motor? does it have a spacer plate on the bottom of the cylinder?

[coolhuh]

I have not checked to see what dome it has. It is a stock '88 engine, no spacer plate, 165lb compression.

[Tom TRX250R]

Yeah I was going to say that compression does seem a little low.

[zedicus00]

actually if its a 21cc dome his compression isnt too far off. is it a gasket or o-ring coolhead?

[coolhuh]

Tomorrow I will be taking the head off and will see what dome it is and if it is a gasket or o-ring.

[coolhuh]

I have a 19cc dome in my cool head. I found a leak in my bottom cylinder gasket, hopefully that is the problem.