What fuel do you choose for 50 year old engine technology

Curious what other 60's - 70's Commando owners are using for fuel and the results realized.
I have a 74' 850 and seeking an alternative to Ethanol which offers barely adequate performance/longevity even with stabilizing additives.
I have been running 105 Octane aviation fuel and my bike loves the stuff.
Also looking for feedback on the high octane rated Ethanol as well, more difficult to find.

It should run fine on ‘super unleaded’ (or whatever it’s called there) ie the higher octane standard pump fuel.

Even that might be overkill on a stock motor, but I like the safety margin, ie even if some of the good stuff evaporates when stood, you’re more likely to have decent fuel still.

My 11:1 920 runs only on super unleaded pump fuel without issue.

There’s really no need to complicate it by buying barrels of avgas through the back door etc… life’s complicated enough !

Of course… my experience is based on the fuel we have here… not out in the colonies…

Never used anything but "normal" (ethanol) fuel at whatever gas station I happen to visit when I need fuel. Bike has been running fine on ethanol'd fuel since 2006. 89 (US octane rating) works fine on my totally stock-engined '73 Commando. I add stabilizer for storage. Bike has had a fiberglass fastback tank since 2008 with no issues. Tank supplier in UK said tank was constructed with resin that could handle ethanol. I treated it with Caswell sealer before its first fill - they said it wasn't necessary but it made me feel better!

I am fortunate to live in Southwest Florida where there are far more boats than motorcycles. Just about every gas station offers non-ethanol gas or Rec-90 as it is known in FL. I have my Commando plus three other classic bikes and they all do very well with 91 octane non-ethanol from my local station.

Super unleaded pump gas is plenty good.

The ethanol has no ill effect on running.
Ethanol attacks rubber, plastic, fiberglass & will facilitate corrosion.

Save the 105 octane race gas for storage. It's great for that. Running it daily makes the rider feel good, so, that's your call to make.

Ethanol is hi octane, they reduce the octane of the remaing petrol the more they add to retain the octane. Pure ethanol is 109 octane. But ethanol has lots of other issues, enough to use ethanol free if you can get it.

kommando said:

Ethanol is hi octane, they reduce the octane of the remaing petrol the more they add to retain the octane. Pure ethanol is 109 octane. But ethanol has lots of other issues, enough to use ethanol free if you can get it.

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Exactly, like water separation in the fuel tank with the water settling to the bottom of the tank. I know I can use this stuff but there's too many side effects.
I've had ethanol issues with other small engine usage, gummy lines, clogged filter baskets etc. in my ATV's, trash pumps, generators, etc. even with stabilizer added I've had very poor results. I had a Honda technician tell me to stop using ethanol in my Honda generators if I had another option as a fuel source. I drove an hour out to the MFA station and they were not offering any fuel over 87.
The air field where I buy avgas had a big sign on the pumps NO GAS.
Ethanol ages very poorly, at least for me in my agricultural usage. I just wish I had a Sunoco station closer than 50 miles as the highest octane around is 87.

"Exactly, like water separation in the fuel tank with the water settling to the bottom of the tank."


That is inaccurate. That used to happen BEFORE we had ethanol fuel. That's why all the old Motorcycle gas tanks are rusted out in the bottom.

Ethanol keeps the moisture (which condenses out of the atmosphere) in suspension with the Fuel. It is cycled through and burned harmlessly. Just the same way we used Gas line antifreeze for years. We no longer need to use it with ethanol fuel.


Clearly, you are simply looking for people to tell you you're doing the right thing using the race gas.

To be clear, I'm no fan of having corn in the gas either. It goes bad quickly and causes storage problems. All of which are easily overcome.

Also, using racing gasoline with a high octane in a regular street engine that has not been modified (very high compression) to need the very high octane, will reduce your power output.
To understand this, you must understand what octane rating is.
It is the resistance to detonation. This is achieved by slowing the burn rate.

Certainly, if you enjoy the smell, and it makes you smile, by all means enjoy the availability of racing gasoline.

Never had any issues on my MKIII for over 70K miles with regular pump gas, ethanol or not. Bike has always run fine. I do opt for hi-test on my 74, but it has been modded with more compression.

concours said:

Super unleaded pump gas is plenty good.

The ethanol has no ill effect on running.
Ethanol attacks rubber, plastic, fiberglass & will facilitate corrosion.

Save the 105 octane race gas for storage. It's great for that. Running it daily makes the rider feel good, so, that's your call to make.

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Looked into the race fuel offering at w WORLDWIDE TECHNOLOGY track nearby, $100 for 5 gallons of 110 race fuel.

concours said:

"Exactly, like water separation in the fuel tank with the water settling to the bottom of the tank."


That is inaccurate. That used to happen BEFORE we had ethanol fuel. That's why all the old Motorcycle gas tanks are rusted out in the bottom.

Ethanol keeps the moisture (which condenses out of the atmosphere) in suspension with the Fuel. It is cycled through and burned harmlessly. Just the same way we used Gas line antifreeze for years. We no longer need to use it with ethanol fuel it with ethanol fuel.
View attachment 125471

Clearly, you are simply looking for everyone to tell you you're doing the right thing using the race gas.

To be clear, I'm no fan of having corn in the gas either. It goes bad quickly and causes storage problems. All of which are easily overcome.

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Not looking for anyone to tell me what I want to hear or what is right or wrong, just seeking experience of others.

I had been mixing Avgas with ethanol 1/2 & 1/2, and using it in my small engines and motorcycle. These fuel tanks sometimes sit for very long time with moisture absorption taking place after 6 or more months. The airplane mechanic called it phase separation(?) which the Honda tech showed me in a pour off...very thin layer of moisture on the bottom of a clear vile. That fuel had been sitting in the tank before spring and most of the summer. Early following fall that generator would not fire no matter how many pulls.
I had to send my Norton tank out to be resealed after 7 years, moisture in the fuel.
I have been advised by a group of guys that maintain a a B25 Liberator to avoid Ethanol. Use a higher octane fuel with a stabilizer add,
Thus my question/search.
Thank you all for your input.

Lineslinger said:

Not looking for anyone to tell me what I want to hear or what is right or wrong, just seeking experience of others.

I had been mixing Avgas with ethanol 1/2 & 1/2, and using it in my small engines and motorcycle. These fuel tanks sometimes sit for very long time with moisture absorption taking place after 6 or more months. The airplane mechanic called it phase separation(?) which the Honda tech showed me in a pour off...very thin layer of moisture on the bottom of a clear vile. That fuel had been sitting in the tank before spring and most of the summer. Early following fall that generator would not fire no matter how many pulls.
I had to send my Norton tank out to be resealed after 7 years, moisture in the fuel.
I have been advised by a group of guys that maintain a a B25 Liberator to avoid Ethanol. Use a higher octane fuel with a stabilizer add,
Thus my question/search.
Thank you all for your input.

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Your mechanic read "phase separation" off the Startron bottle. It's another brand of fuel stabilizer. The story sounds convincing, but the bottom line is it doesn't happen unless it sits for two years in which case you've got bigger fish to fry….

Not my mechanic, a mechanic who restores WWII aircraft nice enough to share his time.
Thank you for the advice,

Lineslinger said:

Not looking for anyone to tell me what I want to hear or what is right or wrong, just seeking experience of others.

I had been mixing Avgas with ethanol 1/2 & 1/2, and using it in my small engines and motorcycle. These fuel tanks sometimes sit for very long time with moisture absorption taking place after 6 or more months. The airplane mechanic called it phase separation(?) which the Honda tech showed me in a pour off...very thin layer of moisture on the bottom of a clear vile. That fuel had been sitting in the tank before spring and most of the summer. Early following fall that generator would not fire no matter how many pulls.
I had to send my Norton tank out to be resealed after 7 years, moisture in the fuel.
I have been advised by a group of guys that maintain a a B25 Liberator to avoid Ethanol. Use a higher octane fuel with a stabilizer add,
Thus my question/search.
Thank you all for your input.

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Lineslinger,
I just wanted to give you my 2 cents on this. I have a 74 with a shaved head and in all my years of ownership I have never had any problems using hi-octane pump gas at anywhere I need fuel. I live in a place where it doesn’t need to put away for the winter so I have no need for a stabilizer. I like to go on trips where I don’t need to look for a station that has a special fuel.
Mike

Lineslinger said:

I have been advised by a group of guys that maintain a a B25 Liberator to avoid Ethanol

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The B25 is a Mitchell, The B24 is a Liberator - easy to fat finger on a keyboard. Anyway, there's no alcohol in any avgas so I don't know where they're getting their information. I just use hi-test with no issues. The upside of ethanol in fuel as someone else has already pointed out, is that it combines with water so there's no rust in the bottom of the tank. The downside is it's hard on old rubber but there shouldn't be any in our bikes. I have NO problem with 10% left in my farm and other equipment over winter. There are folks looking for a scapegoat and blaming all their problems on ethanol. My Wellcraft had a 300 gallon tank that I used with both 10% pump gas and ethanol free but I replaced all the hoses with the latest USCG approved. That boat with two 454s was fun but $1000 at the fuel dock. Yes, older marine engines, outboards especially, may have rubber that's susceptible. They also may have fiberglass fuel tanks like older Commandos, another reason to avoid alcohol. Avgas is very stable and will sit for a couple of years without a problem. it also has lots of lead, even 100LL or low lead. Yes, it has less lead than the 100-130 it replaced but it still has a lot. It fouls sparkplugs and centrifuges out in prop shafts and crank sludge traps. When one removes a constant speed prop that been in place for hundreds of hours the hollow crank shaft will have a thick coating of lead sludge. One of the maintenance tasks on a Hamilton Standard prop as used on big radials is to remove and de-sludge the prop dome. Avgas has a much lower Reid Vapor Pressure so as to not vapor lock at altitude. It's much less volatile as well which makes for difficult starting in very cold weather. Neither the vapor pressure nor volatility is an issue for our bikes. Lead, however just isn't good for us.

Don't waste your money on $7.00/gallon avgas unless you want to store your bike for extended periods - more than over winter.

If you're able to ride your bike year-round and go thru a tank of fuel every week, then using non-ethanol is less of an issue. I have four classic bikes which are all ridden as often as possible. Sometimes a bike might sit for a month. Sometimes I don't always go thru a tank every time I take a bike out. Knowing I have non-ethanol fuel in the tanks is reassuring.

The WWII aircraft I mentioned is a Liberator, no typo, just didn't ID it correctly. I have a couple photos of my dad and his air crew in England in front of a B-17. He was the gunner in the lower gun turret. Only talked about it once.

The feedback to my question makes it pretty clear I may be causing a lot of my problems by mixing or strictly using Avgas, at least when storing equipment/bike for six months or longer. I can manage the fuel choice in my 850 in accordance with riding habits. As to my farming equipment I need to start draining the tanks before putting gear away for the season.
I don't log as much riding time as I used to, my skills riding are still decent but with today's drivers the roads are more dangerous than ever before.

Thanks to all for sharing information.

In Iowa, where corn is king, we have 91 octane no ethanol available most everywhere. That is what I run and I try to buy it from "Top Tier" stations which tout the detergent additives in their fuels.

Lineslinger said:

The WWII aircraft I mentioned is a Liberator, no typo, just didn't ID it correctly. I have a couple photos of my dad and his air crew in England in front of a B-17. He was the gunner in the lower gun turret. Only talked about it once.

The feedback to my question makes it pretty clear I may be causing a lot of my problems by mixing or strictly using Avgas, at least when storing equipment/bike for six months or longer. I can manage the fuel choice in my 850 in accordance with riding habits. As to my farming equipment I need to start draining the tanks before putting gear away for the season.
I don't log as much riding time as I used to, my skills riding are still decent but with today's drivers the roads are more dangerous than ever before.

Thanks to all for sharing information.

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If using strictly avgas you should be able to store your equipment for a couple of years without loss of quality. Know however that water will separate and settle to the bottom. Fuel with alcohol will combine with the alcohol and burn up to almost 1%. You will notice that pilots routinely sump and sample the low spots of their tanks and the main fuel strainer. Planes with recessed or flush fuel caps that are stored outside often have water in the sumps. Some condensation also occurs from storing with partial fuel especially with metal tanks. Those with rubber bladders like mine seem less susceptible. I also converted to non-flush caps and store in my hangar so no issues.

Here's a long story about water in fuel: Years ago the company I worked for had a Douglas B23 bomber that had been converted to executive transport post war. It was then converted to a flight test aircraft for various airborne equipment. It eventually became disused as contracts bid on didn't get awarded. Every time a contract was bid we'd crank up the Wright R2600 radials and prepare it for flight. At some point it was decided to sell it and because of its weight capacity it was going to Alaska to haul fish. After getting ferry-able it was set to go, it was thought. Our former Air Force hangar had lost its heat and the appointed morning it was below zero but around freezing inside. We pumped the oil tanks full using a full 50 gallon drum of 100 actually fatiguing the bung on the barrel. It got pushed outside, fueled, multiple tanks sumped, and off it took with me and two others in a chase plane. The old bomber, being conventional gear (tail dragger) started down the the runway and as the tail came up all hell broke loose as the trapped water found its way to the engines alternately failing left and right with drastic yaw as the pilots fought it. Eventually one engine stayed running while the other seemed to be making zero thrust - they never feathered the prop. The guy flying the chase Baron had to throttle back as we were catching up fast. After some cockpit drama they successfully landed. I was the mechanic who opened the Lunkin traps and found one completely clean while the other was a block of ice. So what happened is that the engine that eventually ran well swallowed all the water while the other got so much and slowed by some rust that it froze. The sump drains were not necessarily in the best spot for catching water especially in the tail low position.

There - all you never wanted to know about water in fuel. The R2600s flowed about 150 GPH at take-off power.

Then the guys flying the B-23 , after landing, all headed to the hangar for a fresh change of pants.

Great story.

I have a couple of friends who share a small wing over, a "Champ" or Champion I think it's called.
They are religious (with good reason) about checking fuel for water as part of their preflight routine.
Below is a link to the planes and Smart Field where they reside. I can see the airport and planes from the storage shed where some of the larger equipment is sometimes kept, maybe a quarter mile to the east.
Low level flyovers are really impressive, the sound of those engines is amazing.