Premium to regular

[flandersander]

I just bought a rmz 250, and the guy before me always ran premium. I don't have really any access to premium fuel. So to run regular, do I need to jet it up or down, or can I just run it?

 

[flandersander]

Bump. Nobody? Maybe this is in the wrong section?

 

[DaveB]

Not sure what an RMZ 250 is....race two stroke? What year? What does the manufacturer recommend for fuel?

 

[flandersander]

Its a suzuki four stroke racer. They recomend premium.

 

[dooryder]

how do you not have access to premo? as most gas station that ive seen sell 91 octane

and if they recommend it, you should run it, as that is what the engine was designed to run on.

 

[DaveB]

The only way you might get away with 87 octane is if you run at 3000 feet elvation or higher....otherwise, you should probably stick to 91 premium. Got a local airport at Colonsay? Go buy a jerry can of LL100 AV gas and mix 25% with 75% 87 regular....get yer octane and smells purdy.

 

[scoobienorth]

it sucks you just have to buy more jerry cans and plan ahead on your riding, i am in the same boat with my yfz 450 and in my town we have 2 gas stations but no premium to be had, and yes if it is recommended you need it.

 

[flandersander]

The only way you might get away with 87 octane is if you run at 3000 feet elvation or higher.

So its a mixture thing? I do acknowledge your reccomendations, but the closest pump with premo is almost an hour away. I can run premium if I have to, but i would rather just get the local gas, if its possible.

 

[DaveB]

No. It's not a mixture thing....it's a cylinder pressure thing. High performance usually means higher compression. High compression requires high octane. If you are riding at high elevation, the air density/air pressure is less and therefore your final cylinder pressure is lower and you can run lower octane fuel.

 

[flandersander]

Oh. Okay, well thanks for the advice. Are there octane boosters out there that actually do their job? I know my buddies sled needs premium, and when he can't get it, he mixes regular and some alcohol product. Now two stroke sleds and 4 stroke bikes are completly different, but is there something out there? Sorry for all the questions. lol

 

[DaveB]

Most of the "octane boosters" aren't worth the container they come in. Xylene, Toluene and some ATF are the ingredients. When they advertise "raises octane 5 points!" it means from 87 to 87.5. Not worth it. Some guys have gotten lucky with going to the paint store and buying 5 gallon pails of Toluene and mixing 10 to 20% toluene with gas....might try a Google search on that. I found those products too dry and prefer mixing AV gas. If your machine doesn't have an O2 sensor, AV gas will work fine.

Edit: what elevation are you riding at?

 

[imdoo'n]

you don't want to run reg gas when premium is required, as you will soon need some expensive motor work done. the only other option you may have is to lower compression, with extra head gaskets, you may not be happy with the performance. if you can't get premium or av gas as dave suggested, you may as well get rid of the bike, this may be your best option as old premium is not that good either, stay away from octane boosters as they don't work and are very expensive.

 

[atver]

If they call for premium you need to use it.

 

[psullivan]

No. It's not a mixture thing....it's a cylinder pressure thing. High performance usually means higher compression. High compression requires high octane. If you are riding at high elevation, the air density/air pressure is less and therefore your final cylinder pressure is lower and you can run lower octane fuel.

If your jetted right altitude dont matter

 

[DaveB]

Are you suggesting you can jet to compensate for high compression and low octane?

 

[flandersander]

Dave, i'm running around 1500 feet. 15-2000.

 

[psullivan]

Actualy no that is what you were saying.

 

[wienerwater]

Flandersander....not going to get into a long winded debate with anyone over this, but this is what I know for sure.Whatever works for some, and they are happy with it, albeit.Mixing say leaded AV 100LL with unleaded 91, does NOT calculate on a generic math level to obtain a set octane number.AV 100LL here in western Canada all comes from the Imperial refinery in Edmonton, and on a rom/mon (vehicle scale) is about 105 octane.AV octane is a complete different scale then auto fuel.Normally, if you want say 10 gallons of 91 octane, you would mix 8.2 Gallons of 87 (unleaded)octane with 2.4 gallons of 109(unleaded race fuel (VP 113) and you get a more true number.Mixing with leaded AV, you need more, since the leaded AV gas properties does not compute the same, no matter what.This is where guys such as myself running turbo 4 stroke sleds can have issues.It is usually a result of improper mixing, then detonation happens.It is better, (in my case) I run straight 100LL AV, always the same mix.
A good and true fuel booster is "Torco Race Fuel Concentrate".It's not a regular octane booster, but a race fuel "concentrate", and has is a lot of positive feedback.As pointed out previously,Octane boosters that say they raise octane by 5 points, means from 87 to 87.5, not whole numbers.Many people are happy with whatever they do and have positive results, and are entitled to their opinions, and I respect that.I am not here to bash anyone's thoughts.My wife also happens to be a chemical engineer who has worked in some of the world's biggest known oil companies, with a lot of experience in fuel development.
Vp has, or had a similar product, fuel concentrate, but even the distributor advised me to not use it, as they were not happy with people mixing it with fuel from various gas pumps/suppliers.If you have a good known quality fuel station and stayed with it all the time, it would work fine.But some guys would use a good quality fuel one month from the same station, then use poor quality another week from some old gas station and have bad experiences.It's all in knowing you have a constant octane number at the pump when you mix the stuff.
Just my 2 cents.

 

[DaveB]

Actualy no that is what you were saying.

Best read it again....

 

[wienerwater]

This is getting funny now, but I believe on a 4 stroke, the only thing you're jetting it for is the correct A/F ratio for the altitude you are at, according to manufacturers specs.Otherwise it will be running like a rich pig if too fat, or too lean and screw the motor up.Either way, you need the right octane at those specs too avoid detonation,for peak performance.