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.

[nastynotchback1]

I would remove the oil injection and hand mix it anyway.There is no reason to have oil injection on there.You never know when it's going to stop working until it's to late.

[seabeebuggy]

Agree. I may as well on both of my quads.

[seabeebuggy]

OK I removed the oil tank and pump. pulled the piston off. the cylinder does not looked scratched.. I found some metal behind the piston on the case. i sucked it all out. Not sure how much may have gotten into the case. I don't see a way to clean it or a drain plug to flush it. Unless i stand the engine on its end and flush it out that way.. I don't want to split the case if possible.17181078531718107854

[chris p.]

holy molten metal batman !!!!!!!!!!!!!! lol.it doesn't look like it leaned out from the pics but maybe the death rattle did it in(detonation). we always used 100 octane with amsoil dominator and never had a problem.nastynotchback is right.dump the oil injection and premix it.the riders thumb will feel much better too.as far as the oil drain goes I've got one on our 06 preddy 90 so it should be there?? there's a small hole in a crossmember and it should be above that.by the way,what did the spark plug look like when you pulled it? was it intact?

[seabeebuggy]

1718107855
Here is the plug. I have jetted the engine as fat as I could before it would loose power. I drill my jets so i dont know what size they are. Much larger than stock.

[chris p.]

wow.from the pic that plug looks lean.it should be a tan/light brown color but that looks really clean,almost gray.what size carb are you running? when we had our malossi big bore 90 we had a 28mm with 140/45 combo and our ngk iridium 10eixplugs were always good.i always went a little fat on the fuel mix.rather replace plugs than rebuild engines.

[seabeebuggy]

It is the stock carb.. It is on the grey side. It does look lean. The quad has been driven on long trips before but this time was 3 min at best. Higher elevation at that . I I have tuned turbo cars and have lots of knowledge on tuning carbs but It does look lean. I don't know, as i stated I drilled the jets quite large and when it started to run worse I went back to the last jet. Perhaps I need to re tune, after I get a new cylinder and piston.

[chris p.]

dump the stock carb.the stocker is 19mm and parts are non existent.i have a 28mm and a bunch of jets and I also have the malossi big bore 90 that's complete if you're interested.it's in the mini parts for sale section. make me an offer I can't refuse!!!!! it's just sitting btw,what pipe are you running??

[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.

[chris p.]

lt80 is right about compression but with the garbage in the pump gas today we ran 100 just for that fact.don't forget;if you can lessen the chance of detonation with a higher octane you can add more timing and with more timing comes more power so it's not necessarily just the fuel that's going to make the power.it's all in the tune

[seabeebuggy]

how do you advance the timing on a quad? I think i have a aftermarket CDI but don't remember.

[seabeebuggy]

Well I put on a new top end and it runs good. I removed the oil tank and premixd the fuel also put in 104 octane. I put in a new CDI box with high rev. I just need to tune the engine now. This time I will make the mix nice and fat.