It is my understanding that since January 1995 all motorfuels sold in the US are required to contain an additive package that meets the Chrysler 2.2 litre 50,000 mile intake valve cleanliness test and the BMW unlimited mileage exhaust valve cleanliness test. (I may have the tests reversed. It's been a long time since I read the report) Additional additives are usually sales gimmics and are frequently added to the tank truck when they are loaded at the terminal and "splash blended" on the way to the station. Branded gasoline could have been refined by any company. I buy the lowest priced fuel available.

Use the lowest octane you can find.

""splash blended""
Actually, that's truer than a lot of people would believe.
When I was working at a gas station a few years back, I'd often talk to the truck driver. We sold the "ethanol" blend. The driver told me they would put X amount of gas in the tanks and then he would pull up a little ways and they would dump the alcohol on top. That way they could easily control the %.

Some 2 stroke, particularly chain saws benefit by using premium as they have higher compression. Mower engines certainly don't need anything more then regular. Some consideration has been given that a brand may regulate their own premium to a higher guality then regular because it is their premium but that's an iffy thing.

Your handle indicates you are somewhere in nevada as am I but not where. In S. Nev all our fuel come via pipeline from S. Cal. This is all reformulated California grade, basic fuel. If you/re in /the Reno/Carson area I believe you get fuel in a similar manner from the bay area. Eastern nev gets fuel via truck from Salt lake. Eastern nev probably gets the best fuel. The rest of us get California dung and all additives are as already mentioned dumped in the trucks at the tank farm. Who owns the refinery is anyones guess, it all started as the same stuff, California reformulated or Designer Fuel.

In theory, a low compression mower engine will run better on regular. Although only by s amll amount, regular actually has more BTU's then premium.

Buying from a busy station which turns over their fuel supply quickest is really the better idea as old fuel problems are what we see in the shop. However, from my own person experiments when I still has a yard I had to take care of myself, I found that premium gave a hedge in terms of fuel going south from aging. Additives, higher octane, not sure why but for me it seemed to improve the fuel aging caused problems.

This is straight from the B&S care & repair manual. Use gasoline with a 77 octane rating or higher for L-head engines and 85 or higher for overhead valve engines. Since small engines operate at relatively low compressinon ratios, knocking is seldom a problem, and using gasoline with a higher octane rating is unlikely to offer any bendfits. But remember DO NOT USE OLD GASOLINE!!

If you're in Colorado, there are certain branded stations that only get their fuel from a certain refinery. The other companies do have their specific blends which can come from the same refinery and they are all programmed with unique IDs and keyed to a card. The drivers around here swipe their card through a reader at the terminal and that determines what product they can get. I would assume that the other branded stations are the same, but I don't know. I assume that this is the way it works elsewhere, but who knows.
If a driver is caught doing his own 'blending', he and the company are in BIG trouble. Samples are pulled many times a day for the various products as well.
The places you have to watch are the unbranded places like Sam's, grocery store chains and the like. They will just get it where it is the cheapest and who knows what they get.....

"Buying from a busy station which turns over their fuel supply quickest is really the better idea as old fuel problems are what we see in the shop. However, from my own person experiments when I still has a yard I had to take care of myself, I found that premium gave a hedge in terms of fuel going south from aging."
The stations I've worked at in recent years probably went through 94% regular to 6% premium (we won't count diesel). Premium sat in the underground tank much longer than regular.
IF you buy premium for a small engine, get it from a station that has 3 separate hoses on the pump. By the time you "purge" the hose on a single nozzle pump, you're probably getting a qt. of "regular" with the rest of your purchase.

Bill, I won't disagree with you because i don't know but if correct it does say just that much more for the longevity of premium fuel. Maybe premium is just closer to the fuel I bought when I was a kid, that stuff lasted a year without help from Stabolizer.

Thats a great point about the regular fuel getting "turned over" a lot quicker than Premium fuel, I didnt even think about that. Here in Las Vegas,my local gas station is always busy, so I am sure their gas is replenished daily. My lawnmower has been hit and miss on starting lately, I will get some fresh juice today and see if it helps. Maybe toss in some Seafoam for good measure too! (along with the Stabilizer.)

Hewy whizzer; do you happen to have a Whizzer? Great motorbikes.

I'm with Nevada Walrus on this one. I use only premium unleaded containing no ethanol in my chainsaw, and whatever cheap crap I can find in my lawnmower. Big difference in the way those two engines are tuned. If I mix up a batch of 2-stroke mix and I don't use it all up in a month, it goes in the mower.

I'm a little old for motorbikes. Just 2 LBs, an Echo blower and a Husqvarna trimmer.

In Australia, Shell has four grades of unleaded with the following RON values:

regular unleaded 91 octane RON
premium unleaded 95 octane RON
Optimax (TM) unleaded 98 octane RON
100 octane RON (ethanol blend)

I use the 95 octane RON stuff as I understand that the 98 and 100 octane fuel is "denser" fuel, and the carby on my lawn mower is not jetted correctly with this heavier grade of fuel.

A number of Harley Davidson motorbike owners have sworn off the 98 octane stuff as well as the 100 simply because they have experienced problems with their carbys on these premium fuels.

In the US, we use the (R+M)/2 method.
Research Octane Number & Motor Octane Number.
That results in the lower numbers than yours.
I remember 50 years ago we often saw octane numbers above 100 with the "old" method of measuring.

Density between octane levels sounds pretty fishy" to me.
Higher octanes typically have insignificantly fewer BTU's per gallon.

I have done my own little experiment to satisfy my curiosity regarding this same issue. Using a given grade of gasoline has its own pros and cons: Regular gas gives off lower emissions but leads to the engine running a bit louder; premium gives off a lot of exhaust but leads to the engine running quieter; and mid-grade is moderate on both the noise and emission spectra. Although an older engine may be more sensitive to regular gas and would thus do better with higher octane, generally speaking, regular should be fine for most engines. My 1993 B&S 5HP (Quantum) runs excellently on regular. I will say, personal experience shows that the choice of gas brand does matter. Chevron is my brand, and I would not dream of going with anything else. It is excellent with emissions control. I did try discount brand ARCO mid-grade and it was the worst thing ever; the engine emitted soot and it made loud popping noises when it was run at high RPM. If Chevron isn't available, I definitely would recommend a TOP TIER fuel.
If anyone has done or is planning to do similar comparison "experiments," I would be interested to see your results. I'm sure slash-nevada would be interested, too =]

Hello all.

Hi redlandsboy. You provided a great report.
I know nothing about this type of research, but I think you did your homework and I am not trying to find fault within your report.

I have two serious questions.
Was all your testing done using the 1993 B&S 5HP (Quantum)?
Did you have access to a "calibrated emmissions level" measuring device?

Thanks for the Premium grade, Mid-grade and Regular grade fuel info.
You have provided some good FYI stuff. Great job.

Good day.

Thank you for the compliment, rollerzeke. This is definitely something I've been curious over for a long time, so I'm glad I can find a forum to share my experiences.
Yes, all of my testing was done using the '93 B&S. I've heard that the newer mowers have some emissions-control devices now, so my experiences in regards to gas of different octanes may differ from others'. One thing I can tell you is that my lawnmower is VERY susceptible to differences between octanes or between gas brands, haha.
No, I did not have any device to measure emissions level, although I wish I could do experimentation with such a device. My results were based on the color and visibility of exhaust, as well as the scent strength. Honestly, my testing is not as "scientific" as I'd like it to be, but if I ever get the chance to make it more so, I'll take that opportunity.

Just thought I'd share more specifics of what I found when I ran different brands' gasolines in my '93 B&S. I had been using 76 mid-grade for the longest time before I discovered Chevron, and while it is a TOP TIER fuel, it produced way too much exhaust. I'm guessing the age of the engine might have been a factor for the excessive emissions. Shell mid-grade was almost just as good as Chevron for me; it just humored me how the exhaust scent slightly resembled that of diesel fumes. Chevron is by far the best for me; I think its additive helps to produce a somewhat "sweet" exhaust scent, and there's very little "after-scent" once you're done mowing, on regular. It's quite difficult to tell one has even mowed the lawn using a gas engine! One thing I know for sure: I would definitely recommend against going with ARCO. Using virtually any other brand's regular would be better than using their mid-grade. It does kinda go back to the "you get what you paid for" mantra. Even with lawnmowers, I believe that additives do matter... especially if you want to make sure that your lawnmower stays with you a couple more years.

Was just wondering if the 85 octane gas they sell up in Utah is meant for lawnmowers or small engines. I can't imagine anyone puts that into their cars, do they? Do they sell 85 octane in any other parts of the States? Anyone try this gas? How well does it work?

They aren't going to invest in an extra set of pumps to sell lawnmower gas!
Some parts of the country, located in higher elevations, will sell a lower octane fuel as the norm.
Higher elevation means the air is less dense. Ergo, the effective compression of the engine is reduced because you simply cannot get as many air molecules into the combustion chamber on a "normally aspirated" engine as you can at lower elevations.

Yes..I've been told that all gas loses octane over time so premium would last longer before going bad.87 octane is suppose to have more power,more bang, over higher octane,if your motor can run on 87, but higher octane will cool the motor better.I don't know if it's simply colder to the touch,reg. vs. premium, or a molecular thing.I noticed on my Tanaka weed whacker they recommend 89 and have seen 89 requirements on other whackers,chain saws,etc., so that's what I am using but 87 in mower.

Had to laugh but my friend at his river house in Havasu Springs was using up a couple gallons of 110 octane racing fuel in his lawnmower. It ran great,kinda pricy, but worked just fine.

Hello all.

Hi slash-nevada. Did your friend in Havasu Springs use up a couple gallons of 110 octane racing fuel in his lawn tractor, garden tractor or one of the zero turn type units?

It would take quite a long time for my 20" Murray push mower with a thumping 3.5HP engine to use all that fuel :)

Good day.

in his up-right cutting mower, he cuts down his lawn almost to scalp length to let his bermuda grass come in nice, had the mower running for about 3 hours straight. Had to take the clippings away in eight large trash bags.

so are u or are u not suppose to put high octane into gas/oil mix. i have been argueing with a friend about that forever!!!

Yetty, I think it boils down to a waste of money to run a mower on premium, just add some stabalizer to 87 and let er rip. Thanks for everyones input on this.