Before I bought my new car, I’d always fill up my gas can when I filled up my car when the can was getting low. That was when my car used 87 octane.
Now that my new car uses 91+, how would the little Briggs and Stratten engine handle the higher octane? Will it be alright, or should I make a separate transaction when I fill up my car and get 87 for the gas can? No way will I run 87 in my car, either.
I really don’t see a problem. An engines ability to handle a higher octane means it’s less likely to suffer from pre-ignition when using it. In small air cooled 4 strokes this could happen anytime which would mean IMO, you may be better off. You’ll notice an increase in power only if you could adjust the timing to take advantage of it. Otherwise, you should notice no difference or a slight improvement in performance IMO, if the motor was designated for 87 octane use. Air cooled motors seem to be so variable in temperature, you have much less control over pre-ignition then water cooled.
Thanks for not “cheaping out” on your car. We read WAY too many posts asking if it’s OK to use regular in “premium” cars.
The higher octane will not do any harm, but it sure is a waste of money using 91 octane gas in a lawn mower. Please note, the higher octane also will not do the lawnmower any good. It won’t run better on 91.
I suggest the inconvenience of a separate transaction might be worth it. Why waste money on a lawnmower?
The advantage of NOT separating, is occasionally throwing the unused gas back into the car before winter storage instead of throwing it away or trying to store it too long. The biggest enemy these 4 stroke carb. lawn mower engines have is bad gas. Keeping every thing 91could make it less likely to happen.
You can do what I do, going hybrid. I have a gas burning car and an electric mower:)
I have a diesel car and battery powered mower. The motor cycle is gasoline. ?
Agreed, excessive octane rating does the engine no harm, no good either. It’s just wasted money but how much gas does a lawn mower burn annually anyway? I always drained a little gas out of my motorcycle tank to fill the mower because if I bought a gallon can of gas just for the mower, it would go stale before I used it all.
I had a colleague who owned a VW van–air cooled four cylinder engine. He bought the Clark gasoline we used to have in the area–all gasoline was premium at a regular price. He had to have valve work done because of some burned valves and the mechanic claimed that it was due to the high octane gasoline in an air cooled and that he wouldn’t have burned the valves with low octane gasoline.
I thought that this was bull, so, in the interest of science, I ran my lawnmower on high octane gasoline (I also thought I wanted to get a new mower that was self propelled). Well, the engine still runs and I have had the lawnmower since 1988. Even though Ben Franklin says “A penny saved is a penny earned”, I don’t think over the summer season that you will go bankrupt using premium in your lawnmower. The lawnmower doesn’t really need premium, but if it is convenient, that is what I would do.
I agree. You get better chance of burning valves with pre ignition from too low octane gas. Why people think higher octane is more volatile, if that’s what the implication is, then We’re both missing something.
I know mine doesn’t use much. Maybe a gallon a year, depending on how often I mow. I have a 2 gallon can and I don’t think I had to fill it up but once last year.
So a whopping 40 cents difference if I kept with the 93 octane.
I have a decent sized yard, and I don’t think I have an extension cord long enough to have an electric mower. I could almost get away with buying a riding mower for the size of my yard, but the push mower works OK; takes about an hour to do it that way.
Which reminds me, I should probably get a bottle of oil and change the oil in the mower before I start using it for the season.
If your only issue is dumping the leftover gas into your car, i would suggest a half a gallon or so of 87 octane isn’t going to harm your car in any way.
The best thing to do is check the fuel recommendations in the B&S owners manual. Or
http://www.briggsandstratton.com/engines/support/frequently-asked-questions/Fuel%20recommendations/
The general public tends to assume that if performance cars require high octane gasoline then the fuel is somehow more ?powerful?. The big difference between low and high octane is the auto ignition temperature. In actuality high octane fuels have a slightly lower heat value. Theoretically, using high octane gasoline in a low compression engine would result in a slight decrease in performance. It?s unlikely the difference would be noticeable.
Whether or not using Clark premium would result in burned valves is hard to say. I agree the explanation seems infused with BS. But, air cooled VWs, especially the vans when driven at highway speeds, were a bit prone to valve problems. Proper and regular valve adjustment was mandatory. Cylinders 3 &4 ran hotter than 1&2. Anything that contributed to higher engine temperatures would shorten the valve life.
Since you didn’t match your automobile purchase to your lawnmower engine octane requirements, you need to modify your lawnmower to accept the higher octane fuel. Have the cylinder head of the lawnmower milled to increase its compression. Have the timing advanced on the lawnmower. Put bigger jets in the lawnmower carburetor. You should also adjust the valve overlap to force more fuel into the cylinder. While the head is off the lawnmower, be certain to polish the ports in the head. The increased compression may necessitate a stouter crankshaft. Your mower will now be able to take full advantage of the higher octane fuel. You will have great bragging rights about the power of your lawnmower in your neighborhood.
If you don’t do these modifications to your mower, you can still use the premium fuel without any effect on your lwanmower, but you won’t have anything to brag about.
Right now, I have very little left in the mower’s tank when I get done mowing the grass as it is, I don’t think I want to force more in there and have to stop and refuel while I’m still mowing.
I was hoping to save the major engine modification for when I find a rider with a blown engine so I could drop a Chevy 350 in it. 
'I was hoping to save the major engine modification for when I find a rider with a blown engine so I could drop a Chevy 350 in it".
Now that would be a real lawnmower. I have a colleague that moved into an upscale neighborhood and had purchased a rider from a big box store. His neighbor was really upset that this colleague didn’t buy a John Deere as that was the “required” mower for this neighborhood. (Honest–I’m not making this up). My colleague finally painted the mower green to placate his neighbors. Youm modified mower with the Chevy 350 would be great in such a neighborhood.
If a Deere is required, I 'd move or paint it orange. Nothing POs a Deere owner more than orange. It’s much safer crossing the road or/and during hunting season.
no mufflers and deciding to mow the lawn at 5am on a Saturday morning would be my response to the John Deere guy. 
How often were the valves adjusted on that van?
I think every 5000 miles was the recommendation.
I’m guessing somebody on the HOA board was a John Deere dealer when the bylaws of the HOA were drafted.
BC.