Leaded Race Fuel

Top of the morning to everyone.

This isn’t much of a question that needs a specific answer, but more of a bone thrown to open up a debate / discussion.

Having transitioned from racing X30s in the US to Europe (now living in France), I had the unique opportunity to have my jaw somewhat hit the floor when I’ve arrived for the first time at the track, in Valence, and inquired where I could buy my beloved drum of racing fuel, to which the shop owner promptly replied “Race gas ?? We run the fuel from the pump down the road for all of our official races here”

What? Are you honestly telling me that my two stroke jewel of Italian engineering does not need 112 R/M Octane leaded race nectar refined from the tears of the Gods themselves?

No. In fact, your X30 will run perfectly fine with regular premium pump gas, unleaded, and without any additives or anti knock agents, which have been largely and vastly banned in Europe. This does not only save you money, but it also saves your health. As you may imagine, standing in a paddock with 150 engines being warmed up on a stand and spitting out lead particles is not exactly good for your lungs.

In paralel, during international CIK events, Panta supplies unleaded “Race Gas”, which is 97 Octane (in R+M/2 values) ergo : pump fuel

As such : Why is this still happening in the US? What is the purpose of using unhealthy, overpriced and “clearly” unnecessary race fuel in two strokes ?

The engines have to be different. There is no way an engine set up for C12 will run on pump gas.

Why do we still run leaded fuel? Because US karting is very slow to change, and leaded fuel is an easy way to prevent detonation. I agree that breathing it is a bad thing, especially for kids.

If we could get 97 octane from the pump I would run that too. Some places use ms98 instead of c12 or 110. 91 is the most common here with a couple stations having 93. Just depends on how far you have the timing advanced.

Coming from Europe (Ireland) myself, my observation has been that fuel “meddling” is a little more pervasive culturally in the US, so spec racing fuels seem to be more common as it’s easier to test. Many racing fuels have a chemical added that helps with testing.

If you have a spec fuel, then it has to be consistent in it’s composition… which is one of the primary purposes of race fuel… Not high octane, but consistency. Lower octane racing fuels are a thing too, I think you can even get as low as 87MON as a race fuel.

Selecting a higher octane fuel as the spec means that all classes can use it, whereas if you specify a lower octane for all classes you can run into trouble.

Lastly, two strokes LOVE lead (or TEL). It acts as a dry lubricant, coating the internals.

Moving from Europe to America it surprised me that leaded fuel was still allowed. It was banned in Europe a long time ago, I think even for recreational use? In the 90’s/Early naughties I used unleaded pump fuel a lot in Formula A, although we moved to a spec fuel from Atol which was easier to test. In retrospect, I should have stuck with the racing fuel for consistency.

I love how leaded fuel smells, but I am surprised there hasn’t been more pushback against it’s use in the US, because… Cancer.

I’ll be frank, leaded fuels put me off racing in large grids, as well as putting my kids out there too. Sure there’s lots of “well leaded fuel didn’t do me no harm” stories out there… but I’d still rather not breath that stuff, even though it smells delicious.

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It isn’t even really its effect on lungs or cancer that brought on a decline in the use of lead worldwide. There is a well-established link between low levels of lead in children and later cognitive deficits brought on as a result.


I have very strong memories as a child of landing in Paris from my home in the USA. The odor that greeted me in the 70’s-80’s was the distinctive smell of diesel. It hung over Paris like a cloud.

In the early 70s, my family had to move from LA because we (kids) were having persistent eye infections that the docs said were from the air pollution.

The diesel emissions scandal does make me wonder how much crap that didn’t need to be there is floating around.

Good point and I have enough of a baseline cognitive defect to begin with :smiley:

I can for a fact vouch that your US spec X30 will run pump fuel just fine as, case and point, my BBS US Spec prepared X30 has been running without much of an issue ever since i have arrived in late 2018, on pump gas. Its obviously easy for me to preach this to you over the internet, and i understand why you may be reluctant to try, but i did not really have a choice when i got here…

Only difference i’ve found is that my H needle is open a couple more minutes in the grand scheme of things, to achieve same target EGT, but that can 100% be down to atmospheric conditions more than anything.

Happy nevertheless that we got a convo going really fast !

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Fully agree on the notion that repeatability and standardization of the chemical components within a fuel, for governance reasons, is 100% justified.

Nevertheless, Sunoco and VP both make unleaded high octane fuel. Why not switch to those ? I get it that business is business and if i can make a penny, i’d also like for you to make a penny if possible and yada yada yada… You aren’t cutting fuel suppliers out this way, but rather just proposing a more sustainable fuel, which (from all the stories here above), seems to be pretty necessary and compelling.

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I don’t disagree. I have seen resistance from some engine builders (and therefore racers) to running unleaded where it comes to two strokes.

It’s a cultural thing ultimately. It does make me wonder how many parents reconsider karting in situations where leaded fuel is pervasive.

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From what I’ve seen unleaded race fuel also costs a fair bit more than a leaded counterpart. Not sure exactly why, but that’s what I’ve seen.

Not to mention that we have states (like Oregon) that has mandated ethanol blend, and for some of us it’s actually more convenient and easier to obtain 110 octane leaded.

I haven’t noticed that, do you have a site we can compare cost?

Mandated blend for racing fuel, or pump?

Pump. In my county, there is only one station that offers non-ethanol.

One thing to note is that we use different octane rating systems on opposite sides of the Atlantic.

In Europe, they use Research Octane Number (RON), which gives a higher numerical result than Motor Octane Number (MON).

In America, we use AKI, which is the arithmetic average of RON and MON, calculated as AKI = 0.5 RON + 0.5 MON.

93 AKI American premium gasoline has equivalent knock resistance to 98 RON European gasoline, and has ever since we went to E10 as ethanol increases RON faster than MON.

Checking IAME’s manuals, all of their engines are designed for pump gasoline. The KA100, Mini Swift, X30 Shifter all require 98 RON. The X30 requires 95 RON (91 AKI), while no specific recommendation is given for the SSE 175. Vortex says that their Rok Shifter, Rok GP and VLR 100 use 95 RON fuel. TM specifies 98 RON fuel for their KZ engines. Rotax specifies 95 RON or 91 AKI for all FR125 engines; I have used 87 octane in a Max without visible detonation. While every currently popular kart engine runs on pump gas there are old modified motocross engines that have compression ratios higher than some diesels and really do require 100+ AKI fuel - if your track bans leaded gasoline, you may have to switch to methanol, which has its own issues but is 120 AKI.

Our fuel has as much ethanol and butane as the volatility and energy specifications can allow, as they are less expensive than petroleum-refined fuel components. Both of them are octane-rating enhancers and it has been at least a decade since I’ve seen a news story about a distributor or station being busted for selling fuel that didn’t meet the octane-rating specification. European pump gasoline doesn’t have as much butane or ethanol as neither of them save their oil companies money like they do here.

Now, can you just take out your 110-octane leaded fuel or 100/130LL avgas and pour in 93? !!!No!!!
Ethanol has a 9:1 air-to-fuel ratio, while butane and most ‘straight’ gasoline are around 14.7:1. You will need to enrich your fuel mixture because what was correct before is too lean now - by enough to cause a seizure if you used to be jetted correctly.

On my new X30, I switched from 110 leaded non-oxygenated fuel to 93, enriched the mixture, and re-tuned on track, then measured how far I moved the needle before getting it correct. It was 15 minutes (1/4 turn) more open on the low-speed jet and 10 minutes (1/6 turn) more open on the high-speed jet. On a Rotax the rule of thumb is 5 jet numbers on the mainjet (from 115 to 120) to compensate for pump gas.

If you are an American track owner and you’d like to get the lead out, go ahead - nothing is likely to go wrong. With this many kids hanging around the pit and driving in tight packs, and studies showing that any amount of lead is worse than no lead, getting rid of leaded fuel can help your image and perhaps benefit your drivers’ health and wallets.


In a few past posts, I’ve stated that you should run as much ethanol in your fuel as the technical inspection will let you get away with. Let me explain, first how to inspect pump fuel well enough to discourage cheating in a club or regional race, and second the advantage of running as much alcohol as you’re allowed.

You can easily tech for ethanol in two ways. The first is to compare the Digitron reading of a sample of the fuel you specified to the competitors’ fuel and specify in advance how far off you can be without disqualification. The second is to get a 20cc graduated cylinder and mix 10cc of the competitors’ fuel in with 10cc of tap water. Ethanol mixes with water, petroleum components of gasoline do not. Water is heavier than gasoline. A clear separation line will form. If the fuel contains 10% ethanol, this will be at the 11cc mark on the 20cc graduated cylinder. If you are worried about someone cheating by using methanol and non-oxygenated gasoline, perform a Digitron test which will be more affected by the methanol than the same concentration of ethanol. If you use clear graduated cylinders, you can also visually compare the color of the fuel samples in 4-cycle classes. If you take 100 10cc samples, you’ll end up with 2 liters of watered gasoline at the end of the day, which is either a hazmat issue or a good way to start the campfire.

Next up is a quick discussion of chemical supercharging.
Gasoline burns to generate 114,000 BTU per gallon, weighs 6 lbs to the gallon, and burns at 14.7:1. So, for 100 lbs of air, you burn 1 gallon of gasoline and get 114,000 BTU.
Ethanol burns to generate 76,000 BTU per gallon, weighs 6.5 lbs per gallon, and burns at 9:1. So, for 100 lbs of air, you burn 1.71 gallons of ethanol, and get 130,000 BTU.
Methanol burns to generate 57,000 BTU per gallon, weighs 6.6 lbs per gallon, and burns at 6.5:1. So, for 100 lbs of air, you burn 2.33 gallons of methanol, and get 133,000 BTU.
The amount of air you can take in is limited by your displacement, engine speed, and volumetric efficiency. The amount of fuel you can shove in is limited only by not pumping your tank dry before the checkered flag flies!

Charles you make some interesting points. However, I was always under the impression the problem with ethanol is in the carburetor. The ethanol eats at the diaphragm and other parts in the carb. How do deal with this?

How did you know this change was “correct”?


I have not seen diaphragm wear or carb component pitting due to ethanol in fuel, but I either run the carburetor dry and choke the engine when it revs up or take the carb apart and clean it at the end of each race weekend. I have seen all sorts of deposits from leaving either racing gasoline or pump gas in the carburetor all winter.

On returning to the pits, I pulled the spark plug and looked at the insulator, which was the same light brown as before. Before that, I tuned the carburetor by feel - for the low-speed needle it has to be rich enough off the corners to respond immediately and not be so rich that it’s soggy, and then it has to be just lean enough to not 4-stroke as the engine reaches its power peak - on an X30 that’s 11000 RPM. The X30 is sensitive to mixture adjustments and an extra quarter-turn rich on either jet is audible. On a Rotax, the engine will misfire or “pop” if it’s too lean. Other drivers use EGT probes for making sure the top-end mixture is right.

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I’ve also had instant oil separation issues with my states particular blends of pump ethanol and non ethanol, is that something common to the United States or anywhere else? And not just for karts, but motorcycle and small engine oils.

As a layman I found this Cosmos (lead) episode fascinating: