Running Avgas 100LL Comments?

17 replies to this topic
  • smashinz2002

Posted July 04, 2004 - 06:04 PM


I have access to 100 octane, leaded aviation gas. Is it ok to run this stuff in an XR650R? Any benefits at all? Just curious thanks for any info!

  • JetPilot

Posted July 04, 2004 - 07:23 PM


Dont know if there are any benefits, but I can tell you the downside. :awww: 100LL burns longer, meaning that you can burn your exaust valve as the mixture is still burning when it exits the chamber. The other thing is the LL, that means Low Lead, but the name was put there to make the environmentalists happy, 100LL avgas is FULL OF LEAD :devil: !!! Meaning you can foul plugs, valves, etc if your motor isnt designed for heavily leaded gas. Personally, I wouldnt put it in my bike....

People usually run that stuff when they have modded their motor with super high compression, etc and they need the higher octane to stop it from knocking :thumbsup:

  • qadsan

Posted July 04, 2004 - 08:04 PM


One of the benefits is that it's more consistant than pump fuel and I believe it stays fresher longer if properly stored. A good oxygenated race gas will yield more power when the bike is correctly jetted, but some of that stuff is pretty harsh. If I was racing and had a bike that revved much higher than the XR650R, I'd probably consider using a different fuel, but the 650r makes most of its power at a low RPM and runs pretty well on pump fuel.

Here's a direct quote from Team Honda's Bruce Ogilvie when he listed various tips from testing and racing the XR650R. I wouldn't take his comments as gospel, but it's something to think about.

"A stock XR650 will run better on pump gas than a high-octane race fuel, which needs a higher com­pression ratio to be effective. (All gas in the Honda pits is Chevron 92- or VP 93-octane unleaded.)"

  • Mainjet2001

Posted July 05, 2004 - 06:00 PM


You can take Ogilvie's word for gospel, trust me.
No one knows more about the 650R than him and his team.
Those opinions were formed from racing, a lot of racing.
The only time they run higer octane is when they pump up the compression.
Their Baja 1000/2000 pre-run bikes ran 110-114 MPH on pump gas and stock compression.

  • smashinz2002

Posted July 05, 2004 - 06:09 PM


Great info guys, thanks alot I appreciate it! Now I know not to bother with trying that stuff. thanks again.
L.L. Posted Image '00 XR650R

  • Husky_Forever

Posted July 05, 2004 - 09:24 PM


But it wont hurt your bike to run unleaded 100 octane fuel such as VP carries. Mag 7 Race Team serves up 100 unleaded to Baja racers without any problems. The secret is unleaded as opposed to leaded fuel here. The higher the octane, the cooler the fuel burns. The XR 650 typically doesn't need more than pump grade 87-92 to run good. But racing, you run what you can get.

  • qadsan

Posted July 05, 2004 - 09:54 PM


But racing, you run what you can get

Nova / blue :thumbsup:
Magna sin / green :awww:
Premium / red :devil:

  • SaltyWalrus

Posted July 06, 2004 - 01:36 AM


I ran 87 octane in mine for the first time. Seemed to pop when under engine braking much more than when running 93. I will definitely stick to 92 - 93 in the future.

  • beer_studd_76

Posted July 06, 2004 - 03:47 AM


1) lead will not hurt a damn thing in your engine, and FWIW, AvGas has less lead than most leaded race gasses.

2) it keeps forever. gone are the days of varnished or gummed up carbs.

3) it works excellent in my 600R.

4) contrary to jetpilot's assertion, AvGas works best (from my own observations and informal surveys) in low compression engines like un-modded XRs and 2 strokes. it tends to run lean and bog in high compression engines.

5) of course you don't "need" to burn AvGas. pump premium works great in XRs, but AvGas works better: better throttle response, easier starting, etc.

6) i run a 60/40 mix of AvGas/pump gas in my 2 stroke. for the sake of convienence i use the same (not pre-mixed) gas for my XR. i've never run it straight.

7) give it a try. just top off your tank once and then let us know how it worked for you. you'll be surprised how full of it the nay-sayers (who have not or do not burn AvGas) are.


Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • beer_studd_76

Posted July 09, 2004 - 03:30 AM


well smashinz2002, do tell us, in detail, how it went.


  • Moredesert

Posted July 09, 2004 - 06:09 AM


Avgas will work OK in a XR600 because it's a hotter runing air cooled engine. The only problem with avgas is it is formulated for aircraft. I had problems making the bike run right with it. Now at WOT it pulled harder and didn't ping when the engine got hot. But on a water cooled engine your not going to see any benefit over good pump gas.

Case in point: I did a trip to Cabo and brought 20 gal's of Avgas for my 600. The bike ran better on 93 Pemex, started easier and smoother than on the 100 avgas.

  • JohnnyAirtime

Posted July 09, 2004 - 11:46 AM


I think we need a petrol expert here....

I'm not one, and I know from facts (read many a thing on this to win a bet 3yrs ago)... that Aviation Fuel is VERY DRY. The lubrication of the fuel sucks for a two stroke or four stroke... and the 4strokes don't benefit one bit.

I'll take a Pump gas Premium over any AVgas anyday. But that's me. Same reason cars/vehicles are made not necessarily to run on Premium... and when you run premium your cars are running richer (unless stickered "premium unleaded fuel only")

Why do you think when you buy a "chip" for your car... making it faster and more performance related, that they require you to run premium?! Besides knock and ping, it's been remapped to run rich, or leaned out a tad for the premium fuel. (come on guys... tell me if I'm blowing smoke here!)

There's a lot of myths about AVGas, high octane fuels and standard pump gas in stock four strokes. I wish someone had all the answers and could put us all in the think tank.

  • JetPilot

Posted July 10, 2004 - 12:03 PM


Quadson is correct about 100LL Av gas. :D Really high octane gas like 100LL sees most of its benefits in high compression specailty engines where pump gas would knock, or in turbocharged aircraft engines. It may run cooler, but burns LONGER, so its more likely to burn your exaust valves on the way out.

Just because some engines need super high octane gas doesnt mean ALL engines benefit from it. :devil: AVGas is probably bad for the XR in the long run with no real advantage other than it having a longer shelf life. But then again I doubt anyone is buying 100LL because they want to leave the same tank of gas in thier tank for a year. So bottom line is no benefit in the way your XR will run, and a very real downside to using 100LL, but there is alwayws someone that cant figure it out :lol:

There is very strong consensus out there that AVGas is just not a good idea in the XR, with the exception of Beer Studd. There is always someone that will get an idea in thier head and twist the facts to fit what they "Beleive". :awww: Personally I respect and listen to guys who are capable of learning and putting aside their misconceptions. :thumbsup:

  • beer_studd_76

Posted July 11, 2004 - 06:21 AM



yup, i guess you're right. my bikes don't run any better on AvGas :thumbsup:.

poor, ignorant me. i must just be imagining the easier starts, and better throttle response.


  • JohnnyAirtime

Posted July 11, 2004 - 07:57 AM


Ez turbo... I was saying you didn't have better starts...etc. Just saying I didn't think it was 'better' for the bike. But that maybe it did more bad than good. :thumbsup:

And I'm for sure no expert in the subject.


  • beer_studd_76

Posted July 11, 2004 - 04:22 PM


i geuss easier starting and better throttle response aren't "real" upsides :thumbsup:

besides that, she's an 85. if i get 19 years of easier starting and better throttle response instead of 25 years of harder starting and so-so throttle response, well then IMO that's a good trade.

FWIW - there is no "consensus" on AvGas being bad. that's just haters like you parroting what you heard some other expert say :devil:


  • smashinz2002

Posted July 11, 2004 - 06:04 PM


Ok, I have found and talked to a guy who is an expert with over 30 years experience with racing engines, airplanes, high octane leaded fuel, and avgas. Here is what he told me about it:
1. Avgas IS a dry fuel and should be mixed with car gas for
use in a stock motorcycle engine. It will evaporate off
your hands like alcohol, leaving no smell.
2. Avgas has more lead than any car gas ever had at any time
3. A mixture of 2:1 will benefit the power output of a
motorcycle engine if said engine is compressing 10:1
or higher, however the avgas additives are for aircraft.
4. Avgas may in fact burn exhaust valves running it
straight, however a 2:1 ratio with car gas will provide
enough protection against that problem for a bike.
5. The 2:1 mixture will also provide the necessary car gas
additives which are also beneficial to motorycle engines.
6. Avgas is formulated for out-dated, very low compression
air-cooled aircraft engines and contains additives
specially made for those engines.
7. Avgas is much higher quality than any car gas
8. Shelf life is only slightly better than car gas. It will
still turn to varnish over time.
9. Running super-unleaded car gas in a motorcycle is the
safest solution, however a noticeable improvement in
upper rpm power output will be noted by running a mixture
of avgas in the bike. Additive protection will be reduced
I told the guy that when I tried a 2:1 mix of the avgas and super unleaded, that my bike did in fact run stronger in the upper revs, but got hotter and spewed a little coolant after I shut the engine off. He said that if I only ride the bike on weekends and don't run the engine for long periods at wide open throttle, then the fuel mix will not damage the engine. More deposit buildup and/or plug fouling might still occur however.
Posted Image

  • JetPilot

Posted July 12, 2004 - 03:27 AM


Mostly good stuff on AVGas Smashinz. As your guy said, AV Gas will help mostly high compression motorcycle engines at high RPM's. If we were running those 10,000 rpm superbike engines, mixing it might help us, but the XR just does not rev high enough to benefit from AV Gas, not even the mix. The fast that team hondas Bruce Ogilvie says "A stock XR650 will run better on pump gas than a high-octane race fuel, which needs a higher com­pression ratio to be effective. (All gas in the Honda pits is Chevron 92- or VP 93-octane unleaded.)" should remove all doubt from this subject. So you get almost no benefit but you do get the valve burning, lead, and other bad stuff.

Beer stud says "FWIW - there is no "consensus" on AvGas being bad. that's just haters like you parroting what you heard some other expert say". Haters ? I dont hate avgas, used it in my plane all the time, but im just smart enough to know that its not for my XR. As as far as consensus, there sure is one heck of an consensus against using it in the XR, just another fact that beerstud is totally wrong about and to ignorant to see. But then again, thats exactly what I would expect from a person twists facts and immagines improved performance to fit what he WANTS to believe is true.

To give beerstud a little credit (which is hard), there are indeed a couple of upsides to AVGas. It has a neat blue color and a pleasing sweet odor... Has beerstud been adding 100LL to his beer as well as his XR ? that would explain a lot. :thumbsup:

Related Content


Engine Loping/Sputtering by tcaldwell

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • 2 replies

ignitech programmable XR650L CDI by brianhare

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • Hot  60 replies

Cle Elum Sunday 5/29: Looking for dual sport tips by TigerTanker

Dirt Bike   Dirt Bike Regional Discussion   Northwest
  • Hot  32 replies

XR650L super moto wheels by greggkklee

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • Hot  28 replies

Post Apocalypse, ThumperTalk style! by Justin Pearson

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  35 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.