Changing the octane rating of the gas we buy

I’ve been having problems with the fuel systems in both of my chainsaws and while I have them serviced regularly every now and then one of them needs its carburetor cleaned.

Unfortunately both of my saws were in the shop when the big storm hit us so I borrowed a neighbor’s saw to do a bit of the cutting I had to do and then got my big saw back for the bulk of it.

When I picked up my saw the mechanic who fixed it asked me what kind of gas I used in it and I told him regular (87 octane) with the 40:1 mix gas:oil. He recommended that I try 89 octane, the mid grade of gas at most stations.

So, I dumped my 87 octane gas (and some old mix) into my truck and went to the station and filled the truck up with 89 octane and filled my gas cans up too. Anne filled her Jetta up with 89 octane too.

My report is that it makes a significant difference: the saws are running better and the truck and VW are running a lot better.

I’ve run nothing but regular through every car I’ve ever had except my first car which was a Triumph TR4A and it took premium. Today I stepped up to 89 octane and I feel better already.

Seriously, I’m concerned about my power tools working well and not needing carb work all the time and I may have found a piece of the reason they’ve been tough to start at times. A season or two will tell.


  1. How interesting – hadn’t really considered this before. What saw are you running? Huskys and Stihls are popular in the UK and I’ve got a lovely Stihl.

    On a similar area, in the UK, the filling stations switch to winter diesel at about this time of year ready for the cold weather. I always notice how much better my car runs on it. I also have a pre-heater fitted to it, and notice how it’s far better once it’s burned through the sludgy summer fuel.

  2. My saw guy says that the ethanol in the gas is what is really causing problems for small engines. He recommends premium fuel as well which he says allows the engines to run a little cooler.

  3. Bill: That’s exactly what my mechanic said, thanks for corroborating it.

    Jonne, Bill, and John: In the US the lowest octane gas (87) is many times a blend of gasoline and ethanol and while modern car fuel injectors can handle this, smaller 2 cycle engines with carburetors have a tough time with it.

    I figured that the mid-grade gas with 89 octane was about the same: a blend of gas and ethanol but with a bit more “umph.”

    I looked it up just to be clear:

    “Octane rating or octane number is a standard measure of the anti-knock properties (i.e. the performance) of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance.”

    This makes sense given what you’ve both said as well.

    Many European cars, like Anne’s Jetta are built with engines that achieve more power at higher engine RPM, you can really feel it as opposed to an American or even Japanese car or truck. My guess is that cars in Finland (do you drive Volvos there Jonne?) are like that too given the cold climate.

    The short of it is that the lowest end of American gas, like many things here, has turned to shit. Simple as that. We use oil based fertilizers to raise huge amounts of corn to feed to cows to make marbleized beef and so, heart disease and we’re now using that corn to make ethanol which is giving our cars and chainsaws heart disease too.

    John: I have two old Stihls. They’re high end saws that have served me well for over ten years. The big one is an 036 with an 18″ bar on it although it came with a 24″ bar, the small one is a very high end “bucket saw” for arborists and linemen, I’m blocking on the model at the moment this morning (used in cherry pickers and for tree climbing). I use the big one for bucking big stuff, the small one for limbing trees I take down. I put professional chains on them without the homeowner safety stuff (they have extremely aggressive bite with serious kickback consequences if you don’t know what you’re doing). I don’t loan them out because of this as they’re tough to use unless you’ve got experience with aggressive saws.

    That’s me, loggin’ in the morning, bloggin’ in the afternoon.

    Damn it feels good to have power and be able to sit here and post this.

  4. Great stuff 🙂 I run an MS-340 with an 18″ bar. I’m also not a great one for lending mine out, as we (presumably like you?) are off the gas grid so rely heavily on wood for fires, stoves, and a bolier. In the UK anyone can walk into a store and buy one – I’m a big believer in the fact they shouldn’t be sold without basic training… I’d love to get a decent log splitter one day. At the moment, I just use a stump grenade and a sledge hammer and feel like I’ve earnt my supper!

  5. John: As you get a bit older a hydraulic log splitter will save your back many times over. It’s another machine to care for but I could never have continued heating our house with wood without one.

    I got one of these ten years ago. It was a rental from a local hardware store but they gave it a 1 year guarantee: they’d fix anything that broke for a year:

    Given that my log supplier (local arborist I trade web work for logs with) sometimes gives me large logs (up to 4′ in diameter) I can’t lift the rounds onto a fixed horizontal splitter so these switchable models are useful for me.

    The deal with log splitters is the balance between cylinder size/power and cycle time. The bigger the cylinder the slower the cycle time.

    If I were in business or if I were splitting for a half dozen households I’d have two splitters: one like mine for the big stuff and leave it vertical most of the time, one fixed horizontal smaller one with a fast cycle time for moving more wood through faster.

    Once you get into using one of these things it’s great: you put on some of these:

    and you zone out to NPR or BBC for hours while making firewood.

    Just so you know, the first ten years we were here I did 3 cords a year by hand. It was an all summer process. Now I work ahead three years and have about 6 split cords in various states of drying at most times, 2 of them being used in the current year. Makes for some very nice firewood.

  6. I run the highest octane in my snow blower mostly because it is such small quantities that the difference in price just doesn’t justify the saving and I also use Mobile1 oil and I add some additives…..

  7. Wow. I’m feeling extremely naive about all this – perhaps John will give me some lessons one day! Amazing that you have the wood in various states mapped out for future years.

  8. Jon: Since I posted this we’ve gone through two tanks of gas in both my truck and Anne’s Jetta and I’m absolutely sure it’s made a large difference. It’s quite possible that not every car and engine will be as sensitive as ours but the Jetta especially (higher compression engine) seems to have quite a bit more power at lower RPM which is where we want it.

    It’s easy to experiment, the only thing that can happen is your credit card will explode a bit faster. 😉

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