Not all saws like Avgas

[rmihalek]

I had a little arrangement with a neighbor who's an electrician. He re-wired a few things in my garage so I could have a dedicated plug for my Silvey sharpener and things like that and I would clean & tune-up his vintage Homelite XL-12.

The XL is in great shape, but needed a little TLC. The craftsmanship on this saw was refreshing: nice little copper tube with brass fittings to carry the bar oil, easily adjustable carb, etc. I see why these were so popular back in the day.

So, I dumped out the fluids, took the covers off, cleaned out all the oily dust. I put in a new fuel filter and carb kit too.

I filled it with my usual mix of 100LL avgas 32:1 with Mobil 2T premix oil. The saw started right up, but after about 10 or 15 seconds it died. I choked it for one pull, then pushed the choke off, she started right up and died again. I could kind of get it to keep running but it wasn't responding to either H or L needle adjustments.

It was getting late, so I figured I'd get back to it the next day. Well, the next day, I tried again and the same pattern happened. Then, I had an idea: what if this old gem of saw was not liking the 100 octane fuel?

There was only one way to find out. I made a mini-batch of 32:1 mix using 87 octane pump gas with the Mobil 2T. I poured out the avgas mix, ran it dry, then added the pump gas mix. She fired right up, idled really smoothly, and after some L and H needle tweaks, revved right up and then idled back down. I brought it out back and cut some cookies to fine tune the mixture and it just kept running great the whole time.

I've been struggling to get a Stihl 050AV running smoothly: maybe it's the avgas?

 

[nmurph]

that jives with what brad has said about experimenting with avgas.

 

[blsnelling]

Did you retune the saw? Retuning is required to run 100LL. The saw should run ok with it, just not idle or have as good of throttle response as pump gas. You're likely to loose a little power as well. Not worth it IMHO.

 

[Tzed250]

.


Any octane over what is needed to resist detonation is wasted and will cost power.


.

 

[Nitroman]

You boys seem to have quite a bit of trouble with the stuff...and I cannot figure out why, as I have never had any problems with the four saws I've run it in (137, 394, and 3120, plus one back in 1990's), but then, these were Husky's. My 175hp Johnson (prop and jet), a 90hp Evinrude (prop and jet), 1994 Polaris 440 Sport GT (stock), 1997 Polaris Ultra SPX SE 680 (stock), 1999 Polaris XCR-800 (very not stock), and an Arctic Cat 570 fan longtrack (stock).

 

[BloodOnTheIce]

In my experiments with fuel a lot depends on the weather, humidity, and temperature all come into play. What will run great on a rainy cool day, won't run for crap on a hot dry day. None of my saws run more than 93 octane pump gas, for the extra cost and hassle of finding it, high octane over 93 octane fuel isn't worth it.

 

[Oldsawnut]

I used to run high test in all my saws but now I can't get it without ethanol. The cennex has no ethanol but only 87 octane so it was a no brainer to switch over to 87 for me. Seems to work just fine with all my saw even the ones with 190psi. Seems like a waste to go for the av gas unless its your only source for ethanol free.

 

[rmihalek]

Two reasons I was using it: a) I know an airplane mechanic who gives it to me for free, and b) it is ethanol free.

When the mechanic has to do fuel system work, they remove the fuel from the plane. They call this off-gas. They are not allowed, by law (state,federal?) to put the off-gas back into the plane. So, they either pay to dispose of it or let yahoos like me fill up as many 5 gallon jugs as I want. Last time (about a year ago) I got 40 gallons.

Normally, he requests that I don't take so much because some local kids with dirtbikes like to run it as well, so he wants to spread the wealth. Well, the local kids weren't showing up and their 55 gallon off-gas drum was getting near full, so he said take as much as I want. I was on that deal fast!

He also drains some sort of catch tank on the fuel truck that usually has a few gallons of avgas along with about a cup of water. We'll run the water plus about a pint of fuel into a separate jug then I collect the couple gallons of gas into a fresh jug.

I agree with Tz, the extra octane is probably a waste in my saws; the compression just isn't that high. If I could get 87 octane ethanol-free, I'd pay for it versus running the free avgas.

 

[TheRickster]

I know some of the lower conpression motors like the Zenoah's will actually make more power on Coleman lantern fuel which I believe is around a 67 octane rating..

Rick

 

[tdi-rick]

I don't know what Tzed found over the years with bikes, but way back in the mists of time (Ok, mid-late eighties) we stopped using leaded fuel of any sort in kart engines (piston port, reed and rotary valved) as we were getting lead balls all over the plug insulator in our engines and they ran better on 95RON unleaded anyway.

After I stopped racing karts Elf came out with their racing unleaded 'pump' fuel which changed the game totally. No one went near AvGas ever again.