Keefer Tested

Questions About Av Gas Answered

Comments (6)
  1. Simple facts are that running avgas in a two stroke is vastly better for a dirt bike than pump gas and way cheeper than any ra e fuel sold. Is there a performance advantage over avgas when running race gas the answer is hopefully yes. Back in the two stroke hay day of road racing we worked with the legends at Kenny Roberts 250 and 500 gp team. They would air freight out fuel all around the world. When they ran out or the fuel didnt show up we drove to the airport and brought avgas……a knowledgeable race fuel maker is unlikely to ever recommend avgas and they trot out the attitude and low revs story. We watched Wayne Rainey and kick ass on that “unsuitable” avgas and set lap records… we ran avgas here untill the government band the use of lead for racing…. race fuel may offer more power but at any level avgas is cheep relaiable quality power at a price that no race fuel can come near.

  2. Will fuel with too high of an octane rating cause lower engine performance? I think that’s a very important question. I’ve always said “run gas with the octane rating just high enough to prevent detonation, but not higher” with the idea that the author sort of suggests: a higher octane rating with cause a delay in combustion. I’m not a chemist nor an engineer so I would really appreciate a definitive answer to this question from an authoritative source.

  3. I’ve used 100LL for years in lawnmowers, chainsaws, and gravity fed motorcycles with no issues. It’s shelf life is incredible, so there’s no worries if you haven’t started the equipment even for years. The gas generator is the perfect example as it may sit for 3-4 years, then fire right up in an emergency. What I don’t know is if it’s harmful to the clear plastic type of fuel lines in a Harley fuel injected motorcycle, or the fuel pump. I was always told that it’s great for anything that burns gas as long as it has clear-pipe exhast, and it’s less damaging then standard fuels. I have had AV fuel stored in plastic fuel containers for YEARS, and it worked fine in any small engine and even high-reach machines.

  4. I own a aircraft and run many two stroke engines. Avgas has many advantages not related to performance of the engine. Avgas has one job and it may be it’s main job. It can never tarnish ever. Fuel systems in aviation are complex and expensive and the possibility of bad fuel in them has to never happen. The fuel lines are deep inside of the aircraft and would be a huge issue to replace as is the fuel bladders which are made of different rubbery materials that alcohol will dry and crack. I was part of a aircraft recovery where the plane last flew in the 40s and the fuel in the plane would probably have run. It also has to resist vaporizing in extreme temps and altitude. It does evaporate in the tank and when it’s gone it only leaves blue die. 100 ll is also higher than 100 octane. It only has to make 100 and no less. It is more like 120-130. In two stoke it will leave mix oil behind if it sits for a long time. That will clog a carb for a while if you don’t have a primer bulb.

    I am currently looking at these posts because I am having a problem with a high compression 250r motor kicking back hard. It will kick back with the ignition switch off! The flywheel, spark plug , coil are correct and it runs great. It just will kick back so freeking hard it feels like you break your foot. I am running avgas and may try pump gas to see if that is the problem.

  5. Not mentioned here: sub-micron byproducts of fuel burn go everywhere and there isn’t a filter you can afford that will collect them. It’s what damages bearings, shortens engine life and gives greater cause to change crankcase oil rather than the filter. These particles cannot escape the oil as they pass through the filter. AV fuel is “clean”, albeit lead rich and has no alcohol which turns to ice at altitude. “Pump gas” degrades in days, avgas takes years. Avgas will not blend with water that condenses in half-full tanks, pump gas does due to the alcohol. Alcohol burns slower than gasoline. Alcohol leaves any mixture as a gas molecule small enough to penetrate plastic/rubber compounds thus the parent mixture degrades less when dormant in metal containment lines and tanks. “Varnish” related to old pumpgas is the accumulation of fuel additives abundant in their purpose in compounding highway fuel. They are absent from 100ll avgas so you’ll not see sludge in the carb of your airplane. You’re more apt to see “clinkers” of lead built up on plug electrodes…enter, MARVEL MYSTERY OIL…
    Most important, keep your fuel tanks full so they don’t make water and if you’re running a two-stroke use Amsoil, not the other one.

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