High Octane

Since I bought my bike (2005 RM250) I have noticed some pinging. It had some head work and a 265 kit put in by Eric Gorr. Eric said that it will be fine to run on pump gas, so i've be using 91 octane with no ethenal. like i said, though, the bike has been pinging.

So today for a Hare scramble i rode in i used some octane booster and the bike rand great (besides getting a little extra oil on the rear fender, but that has more to do with me lugging the bike than with the jetting i think)

anyway, i am wondering what octane gas people are using or what people recommend to get the best results. I know there are a few places around here that sell race gas, but i have no experience with it and would like some direction.

If booster worked then the most you'd need is 100.

Mix 100 octane and your 91 octane 50/50, and you will be good. What ratio premix are you running?

Mix 100 octane and your 91 octane 50/50, and you will be good. What ratio premix are you running?

I'm running 32:1

So when you mix 100 octane and 91 octane at a 1:1 ratio, does that leave you with 95.5 octane? or does it not work that way?

Mite try and raise your main jet one step to get rid of your ping (its detonation).

1 gal of 100 + 1 gal of 91 should be your 95.5. The kicker is how good or how old the pump gas is.

Edited by Padgett
Mite try and raise your main jet one step to get rid of your ping (its detonation).

1 gal of 100 + 1 gal of 91 should be your 95.5. The kicker is how good or how old the pump gas is.

The 91 octane I get is ethenol free premium at the local Cenex gas station.

so going one bigger on the main might fix this?

and it is looking like the only place to get high octane fuel around me is the airport. will that gas work or is airplane gas different?

I like the idea of trying a larger main and you could try moving up to 40:1 or even 50:1. Less oil in your mix equals more gas and that's like going up in jet size. It would also be worth calling Gorr and seeing if he has any records on what work was done to the head (like milled for more compression).

I like the idea of trying a larger main and you could try moving up to 40:1 or even 50:1. Less oil in your mix equals more gas and that's like going up in jet size. It would also be worth calling Gorr and seeing if he has any records on what work was done to the head (like milled for more compression).

I did speak with him and he said that it was originally milled to have more compression but that he adjusted it to be able to run pump gas......

I really don't want to run a different mix ratio. i would rather adjust my jetting to match my mix than change my mix to match my jetting.

so i found a place that sells 110 octane Leaded race gas. is this stuff ok to use in my RM250. I don't know how leaded gas will effect the bike or if that octane is just too high to use.

I could always mix it half and half with 91 octane to get 100.5 octane. will that be ok or will that harm my engine? but then again i'd be mixing leaded with unleaded and i don't know if that effects anything either.

Yes it will run on 110. However, you should change your jetting to run the 110. I did the race fuel many years ago and it was a pain in the butt. What happens when the Dude that sells the 110 is closed? Just cant run down to the store if your jetted to run 110. I also would not mix it, still got to go to the Dude for fuel. Plus it cost 3 to 4 times more per gal. I would make it run on pump gas. Play with the jetting some more and I think you will fix it. Good Luck.

Yes it will run on 110. However, you should change your jetting to run the 110. I did the race fuel many years ago and it was a pain in the butt. What happens when the Dude that sells the 110 is closed? Just cant run down to the store if your jetted to run 110. I also would not mix it, still got to go to the Dude for fuel. Plus it cost 3 to 4 times more per gal. I would make it run on pump gas. Play with the jetting some more and I think you will fix it. Good Luck.

I totally agree with what you are saying but the head has been modified and there is a big bore kit as well, which makes me think that just running a richer jetting might not get rid of the ping. If it was stock compression i would just jet accordingly. and who knows in the end i just may end up doing that anyway.

but if i do just go with the higher octane gas, shouldn't that eliminate the ping as well? i was having a problem with a hanging idle and richened the pilot and now that is all good but i did have a bit more oil on the rear fender than before, i'm afraid if i richen it up more it is going to spooge all over the place.

i'm not saying i'm right, that's just my thought process right now. it's just easier for me to try the higher octane at first to see how it goes. That said i want to make sure that this gas isn't going to blow up my bike.

i don't mind paying the extra right now for the race gas, i figure if the bike is set up for it then it's better to give it what it wants than to "make it work" with something else, if you know what i mean.

I guess my question is what octane would stop the ping with the least change to jetting?

And will leaded fuel harm the engine?

I guess my question is what octane would stop the ping with the least change to jetting?

And will leaded fuel harm the engine?

No leaded fuel will not hurt the engine. As far as octane, who knows?, every bike is different.

But my guess is somewere around 95 should be good....

Thanks I'll give that a try first. If that doesn't go well ill come back to the other suggestions.

I do appreciate all of the help.

if you have easy access to 100LL AV GAS then run it in your 2 stroke. i have an 04 that is as heavily modified as a 2 stroke can be without changing bore and stroke, and it absolutely loves avgas! runs about $5/gallon here in phoenix so i can afford to run it pure. if not, then use some sort of good, brand name booster

octane booster is one of the worst things you can put in your bike.

its rubbish. total garb. NEVER EVER use octane booster. in ANYTHING.

octane booster is one of the worst things you can put in your bike.

its rubbish. total garb. NEVER EVER use octane booster. in ANYTHING.

that is partially true, but all octane boosters are NOT created equal. the cheaper brands, or ones sold in a clear (non light proof) bottle, and ones that claim to give you more than 2-3 points of octane boost are most likely crap and will hurt your engine. there are some that are good quality and ok to run in an engine, but still i would not ever use it for long periods of time. it is only a band aid and should only be done in a pinch until you can locate the proper fuel for your bike.

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