what fuel to use?

[seabeebuggy]

I have a pred with the big bore kit. high compression head. I took it out this week and burned a hole in the piston. The only thing different from the last ride was the fuel. I usually run 91 in all my toys but forgot and used 89. I have oil tank in place too.

[bb49]

fule won't do it when its 91 to 89 your injection doesn't work or a crank seal went bad

[seabeebuggy]

What is or where is the crank seal?

fule won't do it when its 91 to 89 your injection doesn't work or a crank seal went bad

[seabeebuggy]

I have had pistons burn up over octane levels but in cars not atv's. Does the mixing oil act like an octane? If it is just an oil for lubercation I dont see it burning a hole but if it also acts like a octane I can see it as the cause. I just want to understand the issue.

[nastynotchback1]

Post a pic of the piston if you can

[seabeebuggy]

ok I will have to do some work . I have been reading on 2 strokes and it seems the oil stays in the case and the gas evaporates as it hits the engine parts that are hot. Leaving it unlikely the oil will change the AFR. Leaving me to still thing fuel is too low of octane for the engine. I have also read some saying the oil lowers the octane of the fuel by 2 numbers but i cant see this happening as any ol produce will have a higher heat threshold than gas so mixing them will increase the octane levels as higher the octane the harder it is to burn. I have the new piston on the way. Now i need to figure out if the injection is working or just pre mix? I hope to not have to buy a new carb yet. The quad was ripping in the sand with my 240 lbs on it.

[LT80]

I have had pistons burn up over octane levels but in cars not atv's. Does the mixing oil act like an octane? If it is just an oil for lubercation I dont see it burning a hole but if it also acts like a octane I can see it as the cause. I just want to understand the issue.

I've seen this before.
IMO, compression dictates octane. You said it had high compression. 91 is crap for octane (let alone 89) when you have high comp.
Not enough octane and it detonated, thus the hole.
BIG debate on AV gas (100LL). Some love it. I doubt I'd run it.

[seabeebuggy]

I blew holes in pistons with AV gas on 12 lbs boost. Granted the tune was not right but when I got it right I run 94 and boost 17 lbs on a VW bug.
I have a hetric stage 2 pipe.