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91 octane gas in a small engine?

A

Anonymous-0

Well-known Member
I had to get my floating pump fixed. It was running great one day but wouldn't start the next. This was last year and I finally had a chance to take it in. I thought maybe the flywheel key sheared again but it was the carb all gummed up. The guy said to use 91 octane gas as it won't gum up the carb as much. Anyone have experience in this area?
 
Total rubbish there is more "stuff" in high octane. Clean it well and drain the gas when storing it. Jim
 
I used the low grade of gas for my chain saw & other things, it wiped the piston out. Now all I use in my small engines is top of the grade. So far no problems.
 
i agree wtih jan.

if anything higher octane fuel is HARDER to ignite.. thus harder to start in a small engine that doesn't need it.

don't believe me? drain yer tank and carb and lines on yer pull start push mower. run it till it's dry and stalls.

now go hit a store that sells that 104 octane racing fuel.

go build up yer arm muscles starting it. :)

seriously though. the higher the octane.. the more pre det it is. ie.. to combat spark knock / ping / pre det in high comp high compression engines.

ocasionally you see a cooling use for higher than base octane in some engines. but it's paperwork will say.

none of the small yard care engines and simlar I've had ever wanted anything more than 87
 
I have several different small gas engines that don't get started but once a year. And some of them are at an elevation of 9000' I always us a higher octane. Two cycle engines I use less oil mix than is asked for, and a higher octane.
 
This was once good advice but MAY not be these days.

It was once common for so-called premium fuel to contain no ethanol, which is certainly to be avoided in small engines if at all possible.

These days, just about all gasoline contains ethanol in most (all?) locations.

Thanks, feds.

Dean
 
This gas thing get kicked around here ever so often. At this farm we have 31 small gas powered devices like weed eater, chain saws, pumps and so on. We use 87 octane with ethanol and really just do not have gas problems. We wear out some engines but gas just has not been a problem. At season end we do run them low and add staybill .
I know this is contrary to e most post on here but I am thinking the part of the country and gas mix may have something to do with it. If I pick up a saw or weed eater that has not been used say in 6 weeks or so I am not above dumping it and putting fresh gas in but overall just do not have gas related problems.
 
I have a 6.5 HP engine on my log splitter. Manual says to use 91 octane.
Our fire dept just switched to the two cycle ready mix high octane fuel for our rescue tools.
The fuel does not have ethanol in it. It is pricey though.
 
Just use no ethanol gas. it's out there. put in my lexus which is supposed to us 91 octane. got more mpg and costs less
 
Ethanol is known to clean a system, which is good if everything it cleans goes through! I use gasohol in all my small 4-stroke engines, but anything I mix for small 2-stroke engines I use ethanol free premium. Many of my 2 stroke engines are 30-40 years old. I have good luck with most every thing, have one small outboard (4hp Johnson) that didn't run too well yesterday. It starts well and runs pretty well at wot but misses and sputters at min-range. I put some Sea-foam in it and will see what happens. I don't tear anything apart if I can fix it with Sea-foam, I have had good luck with it in small 2-strokes.
 
Around western ny the ethanol free comes in 91 octane only. For the 40 cents or so more I pay per gallon vs. the 30 gallons or so I use a year I go with the ethanol free fuel. That $12 extra gives me pretty cheap piece of mind. If an engine blows up or gums up I wont be able to blame the ethanol. Bill
 
Many small engine manufacturers specify "91 octane" fuel. What most folks don't notice is that the spec is actually 91 Research Octane Number (RON). The pump rating in the US in Canada is NOT RON but rather the average of the RON and Motor Octane Number (MON). 91 RON is more or less equivalent to 87 octane in the US. In other words, regular unleaded gas.

Note that octane has ABSOLUTELY NOTHING to do with the long-term stability of gasoline. It is strictly a rating for knock resistance. It's true that 100LL avgas is quite stable, but that has nothing to do with its octane rating. Rather, avgas must have a Reid Vapor Pressure rating of no more than 7 psi. Auto fuel, on the other hand, may be as high as (I think) 14 psi RVP, but that would be unusual. Refineries raise RVP in the winter and lower it in the summer.

There are a few ways to get low RVP fuel. The surest way is to use avgas. You can also purchase the ready-mixed power equipment fuel in a can. Lastly, if you happen to live in a state or metro area with specific RVP requirements (such as California), your pump gas will comply with the local requirements. You can find those local requirements at the link below.
Local RVP requirements
 
For my trimmer and Dad's chainsaw, I use premium with a synthetic oil. Never had a problem. My brother is the last one to use the chainsaw and he runs premium w/ non-synthetic outboard 2 stroke motor oil. Now the chainsaw is torn apart on my bench with a scorched piston and cylinder....

Not too happy about that one.

The mower (JD 425 w/ Kawasaki) says 87 10% ethanol is fine and I've been running that in there for many years now, and never a fuel problem.

Donovan from Wisconsin
 
(quoted from post at 17:44:59 05/17/13) I had to get my floating pump fixed. It was running great one day but wouldn't start the next. This was last year and I finally had a chance to take it in. I thought maybe the flywheel key sheared again but it was the carb all gummed up. The guy said to use 91 octane gas as it won't gum up the carb as much. Anyone have experience in this area?
Click to expand...

Useing 91 octane in an engine that dosen't need it is a waste of money.To prevent hard starting in any gas engine after a long layup just add some 2 cycle mineral oil to the gas tank before layup,run the engine until the burning oil is smelled in the exhaust,oil down the cylinder and you'er done.I've been doing it this way for years and haven't had a problem yet.
 
The Short Stop chain in my area sells Phillips 66 gas. There is a label on the 91 octane pump that says there is no alcohol in it. I don't know the truth to the label on the pump, but my '71 Cougar sure likes the stuff.
 
I started using premium unleaded about 2yrs ago. It's shelf life is considerably longer then regular. I was pouring out my chainsaw/weedeater gas all the time; now I get to use up the whole batch!
 
I forgot to add. Last fall (ok, late fall/early winter) I dumped out my trimmer, started it, and ran it dry. Then it hung on my wall all winter until 3 days ago. I got some fresh mix, and it fired up on the second pull (full choke, dies before I can switch it, so second pull is without the choke on), just like every other time I start it.

Donovan from Wisconsin
 
I have a little Harbor Freight 2 cycle gen set. It specifys 91 octane gas. When I use regular 87 octane pump gas, it detonates a bit under some conditions (when it surges a bit when I remove a load.) I use a bit of 104 Brand octane improver to eliminate the knocking. I could buy better gas, but hate to have another seperate supply for the small engines.
Long term storage has been good using Briggs & Stratton fuel conditioner.
 
It wasn't hard starting after sitting. The pump has a small gas tank and I usually just let it run out of gas when I go home. I did this last year and another guy came out the next day, added gas and it wouldn't start. I couldn't even get it to fire when I looked at it. I put it away and finally got a chance to take in this week. The gas in the tank had evaporated but there may have been gas sitting in the float bowl as it needed a new one. He also said some jets were plugged and it needed a carb kit. I'm thinking maybe it had some bad and/or dirty gas in it and when it ran out of gas, it sucked a little dirt into the carb and that's why it wouldn't start the next day.
 
Tru-fuel 2-cycle gas sold in almost every major hardware and farm supply store in southern IN is 92 octane has synthetic premium 2 cyle oil pre-mixed in it and has absolutely no ethanol. It is pricey but works every time.
 
I would be more inclined to use 89 octane... Actually, that IS what I use. The more important point is that you use something free of ethanol because that's what's buggering the carb. If all else fails, mix the gas with Stihl/Castrol mixing oil of that spec at 50:1 ratio and that should provide sufficient stability that it won't gum up as bad.

I know many will argue that ethanol is not the problem... and many will say that there's no need to add mixing oil to a 4 stroke's gasoline... all I know is that I don't have problems with 89 octane gas that's been mixed. 93 octane is nothing but hell...

Rod
 
I dug out the engine manual and it says you can use either regular or premium gas and up to 10% ethanol. It's making me think that maybe it was some bad gas or a dirty jerry can.
 
I recently ran out of gas in my 75 dodge truck. I was in Yelm, and a Ace Hardware store was directly across the street. I walked in the store, and bought 2 gallons of Coleman lantern fuel, took it out and poured it in the truck, and drove 5 miles home, to my gas supply. The truck ran normally. No problems after getting reg gas refill.
 
When I had my ranch I had a few small gas engines and a Hesston swather. Leave them set over the winter with gas in them and I had to clean the carburetors every spring. Had a neighbor tell me about a guy that put Marvel Mystery Oil in the tank every time he put gas in. I started putting in about one to two ounces in the small engine tanks and four ounces in the twenty gallon swather tank. Never had anymore problems with the carburetors. I still use it today in the engine oil.
 
(quoted from post at 19:26:54 05/17/13) I forgot to add. Last fall (ok, late fall/early winter) I dumped out my trimmer, started it, and ran it dry. Then it hung on my wall all winter until 3 days ago. I got some fresh mix, and it fired up on the second pull (full choke, dies before I can switch it, so second pull is without the choke on), just like every other time I start it.

Donovan from Wisconsin
Click to expand...

You didn't have to dump the fuel.Just hang the trimmer up and start it up in the spring.The oil in the fuel mix keeps varnish from forming as the gasoline breaksdown/evaporates.Kerosene added to fuel will help with this also.
 
I run 89 octane in everything I have. I don't have any problems with my weedeater or chainsaws. They are Stihl brands and I only use Stihl 2 cycle oil with nothing else added. They start every spring and run all summer. I always use a funnel with a screen when I fill all my small engine equipment.

To Each His Own I Guess...
 
I know of 2 independent small engine shops shops within 10 miles of here that refuse to warrenty any work done on fuel delivery-carberation systems when used with fuels containing ethanol.
Right or wrong, I don't use it in any small engine which means buying the 92 octane. I only use maybe 40-50 gallons a year total so the added cost is minimal.
 
That seems to be a very convenient way to avoid doing ANY warranty work. Unless you have receipts from the purchase of pre-mix gas, you have no way proving you didn't run E10 gas. And I would not take any fuel dealer's word about his "ethanol-free" gas; if you haven't tested it yourself you have no way of knowing if fuel is truly ethanol-free.
 
Its really interesting the wide array of experiences with small engines and gasoline. In my case maybe I run the small stuff enough, even the seasonal ones, to combat any issues with fuel and carb problems, for many years I've never had much trouble, though my snowblower gave me a fit one year, carb issue, figured I'd have to open that one up, but it was a fuel issue and resolved itself, runs like new and just like when I got it in '02.

I run Stihl 2 cycle 50:1, my saw and trimmer are fine with that, I am very careful to swish any remaining oil out of the container with a little gasoline and make sure to measure or not overfill the 50:1 container with gasoline, being that is a little leaner than the 40:1 that was more common before.

I use 93 or the highest octane fuel, but mix Startron additive into it every time, just for the small engine equipment. My Stihl saw seems to be fine with it. I don't know if the Startron is a snake oil, or something common repackaged, but in things that sat for one year, my tiller started on 1 pull, with the choke on, of course these are stored in a heated garage too. Old ford ranger has 1 year old startron treated gas in it, starts just fine.

With the 2 cycle engines, I know lean mixes and running the heck out of them in hot weather and or similar can be detrimental to engine life, but with mine I don't run em flat out full throttle, yet I don't lug em down and load em up either, kinda clear em out every so often with some brief high RPM under a load, seems to work.

I don't recall any issue using higher octane fuel, a Stihl rep mentioned it was fine with the saw, seems to start easier, though it is tempermental sometimes, I put in a new fuel line, likes to shut off sometimes, but it has to be the saw, fuel or spark problem to sort out, not the fuel. I can't find any ethanol free fuel here anymore, but I really never had much trouble with E10, some fuel lines in older equipment failed, but it might have been more of an age thing, really hard to say what is what with all of this, but from reading.
 
Small engines will run fine on ethanol. That's not the problem... The green sludge it leaves in the carb jets after an extended period of not being used IS a problem.
For what it's worth... I find that if you remove the spark plug and wet prime the engine, then keep a bottle handy to run down the carb throat you can normally keep them running long enough that the vacuum will pull the crap through the jets.
We had a lot of problems with this at the fire dept on our pumps and fan because they weren't getting run often enough...

Rod
 
I would like to think if the state stautes require a sticker stating: "NONOXYGENATED GASOLINE. FOR USE IN COLLECTOR VEHICLES OR VEHICLES ELIGIBLE TO BE LICENSED AS COLLECTOR VEHICLES, OFF-ROAD VEHICLES, MOTORCYCLES, BOATS, SNOWMOBILES, OR SMALL ENGINES ONLY." that more then likely the fuel better be what it says it is. My local experience has been nothing but great with local shops to HONOR the warrentys on any type of work they have performed. Their experience has not been positive with the use of ethanol. Some of them with 25+ years in the business have certianly seen the signs of differnt fuel use on various internal components. proof or NO proof
 
Best to use what's recommended for a mix. Slightly rich is OK but too much oil in fact leans it out more than not enough oil.
 
I have worked on small engines for over fifty years, and it certainly sounds like most of you have good suggestions.
However, in the last few years, I only run Ethanol free high octane 91 or 93 in all my small engines.
I feel it is a small price to pay for better gasoline considering five gallon will last quite a while.
When I purchase fresh gas, I immediately treat it with Stab-Il. Even if I will probably use it within a few days.
 
Agreed. And its not like stale gas is a new issue either. Ethanol doesn't store well especially in the small amount in float bowl. I wouldn't let anything sit for more than a month without treating it with Stabile or Seafoam.

As for 91 octane - why would you ever "need" that in low compression engine?
 
(quoted from post at 17:55:07 05/18/13) Agreed. And its not like stale gas is a new issue either. Ethanol doesn't store well especially in the small amount in float bowl. I wouldn't let anything sit for more than a month without treating it with Stabile or Seafoam.

As for 91 octane - why would you ever "need" that in low compression engine?
Click to expand...
Most of my small engines are OLD. Some of them have nearly 200 pounds of compression---Stihl 200t has 185# Not exactly considered low compression.
You are correct in that I probably don't need 91 or 93 but where I buy gas, 87 and 89 have ethanol and I certainly don't need that!
From experience, I have decided that todays gasoline is not formulated for yesterdays engines! Older automobiles with higher compression, run much better with 91 or 93 although most people will use 86 or 89 and live with it.
 
not a universal rule mind you.

some machines actually specify a higher octane for specific reasons.. on ones that specify a low octane. I usually shoot for it.
 
Based on that wording, I'm going to take a wild guess that you're in the People's Republic of Minnesota. If so, then that labeling is required on any pump which dispenses ethanol-free gas. But there's no law that says the dealer can't also paste it on a pump that dispenses E10. Correct me if I'm wrong, but I don't think your state requires labeling E10 pumps, only pumps that dispense straight gas.

What was it Ronnie Reagan said? "Trust but verify." If you don't want to test for ethanol, then your best bet is to assume you're buying E10 and go from there.
 
LOL after the last two weeks of MN's legislative "accomplishments" I'm rather ashamed to admit living here. yup Ron had it right on!
 
Hey Soundguy.

Perhaps I am all wet but what I was taught about gasoline was that higher octane fuel burns slower than lower octane thus it is able to be used in high compression engines.

I is a trade-off because the high octane fuel has somewhat less energy than lower octane fuel.

I never heard of anyone who had any starting problems with high octane racing fuel compared to regular pump gas.

Just my 2 cents.

Brad
 
ever see a sticker on a race pump that says you may exp hard starts on cold engines?

the race pump in the town up from us has this warning.


as you say.. it IS intended for high comp / high rpm / or performance engines to prevent pre combustion and spark knocks.

sounds like your post did nothing but agree with me right up untill the starting issue.

I don't buy 6$ 104 gas because I don't have anything that uses it. I'm still buying 4$ diesel for my trucks. and 3.59 87 octane gas for my old tractors... Just looking at the logical extrapolation of what a higher octane fuel does. coupled witht he warning stickers on the pumps is what makes me think there might be an issue / waste, running a much higher octane that your engine is requireing.
 
If you want to stop the problems with small engines that set a lot go by your local airport and buy a five gallon jug full of 100LL aviation fuel. I have been doing this for years and use it in everything from cranking engines on large Diesels to chain saw and weed eaters. It has a small amount of lead in it and no ethanol and the higher octane seems to fire off almost instantaneously.
 
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