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Octane, Non-Ethanol and Pinging problems


Jan 17, 2001
Ok, I haven't ridden in a long time and actually got the chance to ride this past weekend (be easy on me =) ). With all the problems Ethanol has been causing, I decided to use the Non-Ethanol fuel at my local gas station. (Bike in question is a 2000 YZ-250 2-stroke, totally stock). I bought it not thinking I'd have a problem with the octane rating. They only sell it in one octane and that's 87. I thought not having any ethanol would be better than 93 with ethanol. Well, I was wrong. The bike was pinging when I rode it so I just took it easy so it wouldn't ping and then called it a day (I maybe just ran about 1/3 a tank through it so there should be no damage done). When I got home I drained the tank and went out and got some Royal Purple octane booster and added it to all my fuel so I will run the octane boosted fuel next time I ride. If it even does boost the octane like it says it does.

My question is this. Will the booster help or should I just be using 93 with ethanol in it? If the booster is bogus, should I just add some 93 gas (and oil) to what I have? I just don't want to have to constantly be draining my float bowl and tank and be worrying about little seals getting eaten by the alcohol.


Jan 17, 2001
Anyone have any advice on this?
Jul 27, 1999
Anyone have any advice on this?
Mike - It really depends on what the component makeup of the octane booster is, where in the fuel distillation curve it will exert it's octane effects and what the root cause of the detonation really is. That's a long winded way of saying do a few test passes under load using the octane booster and see how it goes. It's easy to pick up evidence of light detonation on a clean plug. It will look like little black pepper specs on the nose of the porcelain.

Of course (and you knew I would get to this) the better long term solution is to get a small quantity of good leaded race fuel and cut that pump swill with it till you have a workable safety margin. If the ethanol was enough to keep the detonation in check then it shouldn't take too high a percentage of real fuel to prop up the pump gas.
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Jan 17, 2001
Thanks, Rich. I was waiting for your response because I know I'll get good info. Thanks for the description of what to look for on the plug. I'll look at that tonight.

My plan for tomorrow (if I can ride) is to try what I have with the booster in it and see if it pings. If it still pings, I'm going to drain my tank and fill it with 93 (with ethanol, yuck!) and verify that the pinging is gone and then I can dilute my 87 stuff with race fuel for the next week.

Let me ask you this, Is the ethanol really as much of a problem as I am thinking? Is everyone else using it and not having a problem or do they all use race fuel? Is my fuel system going to get eaten up if I leave it in there or do I need to drain everything every week? I hate ethanol.


Jul 29, 2000
South America
Royal Purple octane booster definitely works.
If you don't like changing crank seals twice as often then don't use gas with alcohol. I made that mistake and now totally swear off every drop of alcohol. But I've heard some seals have resistance against alcohol, the newer ones but I don't know at what year they updated the material seals are made of. You should ask the Yamaha dealer. My seals are the old type.
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Jul 27, 1999
Mike - In the 80s when ethanol was relatively new, it's solvent properties could cause some real issues with rubber parts. The OEMs addressed that long ago, but ethanol has other potential issues. A fundamental characteristic of ethanol is it's tendency to absorb moisture from the air. This can be especially problematic on an MX bike as water has a higher specific gravity then the fuel so water will sink to to the bottom of the tank. In short you have to take special care in the way you handle the fuel and store the fuel. From a tuning stand point ethanol tends to make for crappy throttle response and hard to tune out flat spots.

Toulene based boosters like the stuff Maxima used to sell tend to have decent results in two-strokes if you don't get too greedy. Metal based boosters containing MMT (fairly common) will color the plug in a way that will confuse you beyond description :)

Sorry it took so long to respond to this, I must have missed it when your post first hit.

If you're bored and want some likely outdated info on octane boosters here are some specifics I posted a few years back :

I've never liked octane boosters as a substitute for race gas, but given the number of people who send e-mails asking about them it's apparent that people want to know more. They will never replace the real thing, but octane boosters can be useful at preventing knock if you only need to raise the octane a few points, but they come with a host of caveats.

The pros:
- Conveniently located at your local dealer or auto parts store
- Easy to transport
- They are cost effective if your octane needs are minimal

The cons:
- Most boosters raise the RON octane more than the MON octane, which
makes them fairly useless for most race applications, or high load
high heat situations
- Most of the better additives at this point are either Toluene or MMT
based. Toluene has the advantage of being relatively cheap, and fairly
effective at raising the octane even in fairly high percentages. Plus
it has good resistance to pre ignition which is an important consideration
in a two stroke. The downside is as you raise the percentage of Toluene
(or most aromatic hydrocarbon based additives) , the throttle response
quickly becomes flat and mushy. The snap goes BYE BYE.
So the engine won't knock, but it probably won't run worth a damn either.
- MMT based boosters (the most common today) quickly reach a point of
diminishing returns (i.e. the more you add the less it helps)
- Organometallic boosters like MMT can cause a huge increase in engine
deposits, and increase the risk of plug fouling and pre ignition
- Most boosters tend to kill the throttle response and make it
difficult to jet. Mix in the constantly changing base fuel your mixing
it in and you have a constantly moving target.
- Most octane boosters (especially toluene based) have high solvent
properties which can raise hell with reeds and crank seals in two-strokes
- If you need to raise the octane a significant amount, octane boosters
are much more expensive and much less effective than race fuels

There's more to it than this but I'm sure you get the point. Basically
it boils down to this, if your engine only needs a small increase in
octane as a safety margin then using octane booster is still better than blowing it up, but you'll likely give up throttle response for the
convenience. If you need a large increase in MON octane you won't get it from octane booster without paying more than you would for real race gas in the first place, plus it will run BAD. No snap, and an impossible to read plug.

During some testing with VP "Octane Power Boost" (MMT based) on my YZ417 (13.25 :1 CR). I've also noticed a reluctance to start when the engine is cold, although this may be application specific. The throttle response isn't as good as running
VP-C18 or C-12 but it doesn't knock, and the power you give up on the top end would only be noticeable to guys running flat out all the time.

Even though I hate to recommend octane boosters, if you have to use them here's some things you can try in order of my preference based on my testing on a 92mm stock compression YZ400, and a 94 mm 13.25 compression YZ417. I used Amoco Premium MTBE based (non-alcohol) as my base fuel in all tests, which were done in fairly warm 80-95 degree weather. My results probably aren't really useful to anyone who isn't running a similar combination, but they hopefully will shed a little light on the subject.

VP - "Octane Power Boost" - MMT based mixed 1 OZ./gal.
Pretty good throttle response once you get the jetting sorted out which tended to lean out on this combination. This was probably the closest to good race gas that I've seen. Raising the percentage of VP quickly killed the throttle response and made it much more difficult to start cold. This would be a reasonable choice if you can't get race gas or just feel cheap. Street price $10 for a 16oz bottle.

Snap "The Outlaw Racing Formula" - MMT based mixed .75 OZ./gal. Reasonable throttle response not quite as sharp as the VP additive but close. Jetting tended to lean out on this combination. Raising the percentage killed the throttle response and made it much more difficult to start cold. This is easy to find at most auto parts stores and speed shops. Street price $10 for a 16oz bottle.

PJ1 - "Gas Energizer Octane Plus" Toluene based mixed 2 OZ./ gal.
Throttle response is fairly soft when mixed at 1 OZ./gal and gets worse as you increase the percentage, jetting tended to less sensitve to this additive. Top end pull was a better than the MMT based additives at 2 OZ./gal. I've heard that this product has been discontinued, but no confirmation at this point. Street price $6 for an 18oz bottle.

Maxima - "Hi-test Octane Booster" mixed 2 OZ./ gal.
This appears to be a Toluene based additive, but Maxima doesn't list the specifics in their literature. Like the PJ1 additive throttle response is fairly soft when mixed at 1 OZ./gal and gets worse as you increase the percentage, jetting tended to be less sensitve to this additive. Top end pull was a better than the MMT based additives at 2 OZ./gal. Street price $4.50 for a 16oz bottle.
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Aug 4, 2000
@Rich Rohrich , it looks like VP isn't making C18 any longer. I can't figure out if they renamed it or just cut it all together since I can't even find the specs for it to compare. I just picked up a 2019 YZ450F. I've been using C12 in my YZ250 which Eric modified so many years ago. You think C12 would be a good fit for the 2019? I'm in the same situation as the OP, don't want to use ethanol fuel and the non-ethanol is 87 around here. Based on what I learned from you over the years, I don't want to over octane so hoping the C12 is a good fit so I don't have to buy different fuels.
Jul 27, 1999
C12 will likely be an excellent fit for the new bike. It's a great wide range fuel. VP T4 might run sharper with better throttle response but the only way to know how close either fuel is to the existing map in the EFI is to do some testing.
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