The effects of bad fuel/low octane

[Cliff R]

Couple of weeks ago I decided at the pump to fill the gas cans up with 89 octane instead of 93. I was in an el-cheapo mode that day and thought I'd save myself a couple bucks.

What a mistake! I ended up dumping the 2.5 gallons of mix and refilling the can with 93 octane. It started out with my SRM-230 string trimmer. I filled it up and it just wasn't running right and would BARELY idle. I turned up the speed screw and finished the yard.

Couple of days later I was clearing some tops off my quad path left over from logging and my CS-510 would barely stay running and it was stalling against the clutch like it had lost power/low compression....WTF?

Then I decided to till the garden and my Echo tiller didn't want to run for ****! I had just topped it off with the new fuel mix. By this time the bell goes off (ya I'm a little slow at times to pick up on things) and I remembered filling the can at Kroger's fuel station with lower octane.

So I dumped all that fuel and re-filled over at Sunoco with their highest octane. Dumped all the fuel out of the saw, tiller and string trimmer, refilled with the new higher octane fuel and low and behold they idle fine and power is restored.

Not sure at this point if it was just the lower octane, or bad fuel, or combinations of both but thought I'd put the info up here as it might help others out troubleshooting some of their power equipment that isn't up to par........Cliff

 

[BJD85]

Is it possible if you re-tuned your carbs for 89 octain or whatever they would have run correctly? Is that a thing?

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[Mad Professor]

All my small engines get non-E10 premium, 2- and 4-stroke.

Tune may change with different gas. In saws I usually run 100LL AV gas, non-E10 premium if I'm out, always the same mix oil. I keep a tune log for each saw that have run both fuels, so I can tweek the carb if needed without wasting time.

Old mix goes into my 9N Ford tractor, then diluted out. That 9N will swallow about any fuel fine.

 

[Huskvarna hotellgäst]

Husqvarna documentation warns of pre-ignition in their saws if less than 90 octane is used. Other brands specify no less than 95.
I wouldn't have thought that the difference in calorific value between 93 and 89 would cause the kind of performance hit described unless the pinging was so pronounced as to be loading the engine.
(Fortunately, 89 is not sold in Australia. We have 91, 95 & 98.)

 

[BJD85]

Thats true. Just found out my saw requires 91 or higher. Thanks for saving my life!

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[Cliff R]

"Is it possible if you re-tuned your carbs for 89 octain or whatever they would have run correctly? Is that a thing?"

Nope, tried to re-tune the CS-510 by increasing the idle speed and tweaking the L and H screws and it still "bogged" down in the cut if you pushed it hard. It was down on power at least 30 percent leading me to believe the fuel was not only low octane but not any good right to start with.

With the 93 octane I had it out yesterday and flawless, tons of power. Matter of fact the logger who was working my property made a comment that the little Echo was a "good running saw". He owns an arsenal of 660's and a couple of "clones" with Stihl OEM top ends on them.

His newest two 660's are some sort of fuel injector or computer controlled. He was telling about the "drama" with them yesterday but that's a story for another thread........Cliff

 

[Cliff R]

As far as E-10 vs non-ethanol for sure go for the non-ethanol if it's available to you, at least for small power equipment. I move enough fuel thru my stuff that I have zero issues with it as far as clogging them up with "apple jelly" from the water it soaks up.

It helps that I work on this stuff for a living, mostly carburetors and some small power equipment, so I get to see the results of letting this stuff sit for months or even years with E-10 in it......UGLY!........Cliff

 

[wrcho]

Maybe water in the fuel? If you still have any of the Kroger fuel, pour some into
a clear (gatorade or spring water) bottle. Look for that nice cloudy white liquid
in the bottom. A little 2 cycle oil in the fuel helps to see the layer.

 

[Mad Professor]

Madsen's has a good link to piston failure, w/pictures of damage caused by detonation/low octane fuel

http://www.madsens1.com/saw_piston_fail.htm

 

[Cliff R]

I dumped the fuel, didn't even dawn on me to test it for water content. Kind of funny but the full tank from the string trimmer went into the burn-barrel. I stayed way back and thru a lit piece of paper into it then ran for my life........and little to nothing happened. It eventually caught fire but no big "whuff" or mini explosion like I was expecting.

Good new is that power is restored, everything is back up and running like it should be, and lesson learned. That is the very first time I've went with anything less than 92 octane for my 2 stroke stuff and I also believe the fuel wasn't any good anyhow.....

 

[grizz55chev]

I dumped the fuel, didn't even dawn on me to test it for water content. Kind of funny but the full tank from the string trimmer went into the burn-barrel. I stayed way back and thru a lit piece of paper into it then ran for my life........and little to nothing happened. It eventually caught fire but no big "whuff" or mini explosion like I was expecting.

Good new is that power is restored, everything is back up and running like it should be, and lesson learned. That is the very first time I've went with anything less than 92 octane for my 2 stroke stuff and I also believe the fuel wasn't any good anyhow.....

I aways empty the tank of the machine I’m working on to check for contamination, saves a lot of chasing yer tail. A quart jar works well.

 

[CR888]

Mmmm...the 'presumption' that these running conditions are based on octane change I'd be weary of. Sounds like that fuel had more issues besides octane.

 

[NSEric]

I've seen lots of similar issues when running regular gas in small motors.
It's not just the octane, there's different additives in it too, the motors don't knock like they need more octane they stall or run badly like there's water in the gas.
I try to buy non ethanol premium for my 2 stroke bike and saws.

 

[Totembear]

Probably a high content of water in the fuel. Like said before, the octane rating wouldnt make that much of a difference in performance. You might have to tweak the carb, but thats about it.

 

[Chainsaw Jim]

Lower octane burns faster and will advance the ignition timing. You should be able to take a known de-tuned model like the ms360 and get a boost in power running 87 octane.

 

[TRTermite]

Maybe water in the fuel? If you still have any of the Kroger fuel, pour some into
a clear (gatorade or spring water) bottle. Look for that nice cloudy white liquid
in the bottom. A little 2 cycle oil in the fuel helps to see the layer.

If you wish to check for alcohol put a inches of gas in a clear bottle then add a bit of water let it sit and watch to see if wateron the bottom stays separated from the gas floating on the top OR if a third quantity show up in the middle of the liquid. If there is alcohol in the gas it will start to blend (separate from the gas) with the water creating another layer of liquid between the gas and water.

 

[sb47]

Sounds to me like you just got some bad fuel. I run what ever from 89 to 105 octane with zero issues. 3 octane numbers shouldn't make any real difference in performance and you shouldn't have to re tune when switching between the two.

 

[SteveSr]

Sounds to me like you just got some bad fuel. I run what ever from 89 to 105 octane with zero issues. 3 octane numbers shouldn't make any real difference in performance and you shouldn't have to re tune when switching between the two.

+1.

In the majority of gas stations the mid-grade (89 octane) is formed by blending the 87 and 93 octane fuels in the correct proportions. This practice saves the need for a separate underground storage tank and all of the monitoring and compliance costs that go with it.

However a few stations have a dedicated mid-grade storage tank. I would think that mid-grade would not be a high volume seller and product would likely sit in the tank for far too long. Next time you are at the station take a look at the storage tank fill manholes. They should be clearly labeled as to product type. I wouldn't have thought that Kroger would have old fuel issues as their price is usually the lowest. However, it does sound like you got hold of some old/bad fuel.

 

[Ted Jenkins]

My experience in many many years with saws is that they are the lowest compression and lowest performing motors on the planet. Other race motors are a whole different matter. You can put in almost any junk you can find and they run just fine. That being said does not mean that saw motors do not need adjustment or tuning. Just like pretty much all 2 stroke motors they need to be tuned for what and how they are being used. I recently was given a few gallons of Yamalube so decided to mix a few cans to see how it would work. My first batch was at my normal 34:1. At least one saw did not idle or perform as well under load. I kept thinking since it was smoking that it was too rich so finally pulled the plug. To my surprise it was too lean. The oil worked better than the Lucas that I had been using. So to get better results I mixed about 40:1 and made the fuel mixture more rich. The saw immediately purred like it was perfect. So any small changes to the fuel often will mean dramatic effects on the saw ability to function. Since saw motors are low compression any one living above sea level will not find the use or need for fuel exceeding 87 octane. Yes there are always some exceptions, but few. As the use of a saw increases in altitude the need for higher octane decreases and the need for more advance timing increases. The higher altitude will cause fuel to burn slower thus a few degrees in timing will help restore lost power. BTW I have never had any issue with fuel containing 10% alcohol actually it is the perfect use for chain saws. The fuel stays perfectly dry at all times so is always more clean than pure petroleum based fuel and the motor will run consistently cooler than straight gas. On the negative side fuel with alcohol can not be stored well because the alcohol will attract moisture and thus will mess the tuning of any motor much more. Thanks

 

[Huskvarna hotellgäst]

Two-stroke chainsaw engines have low static but high dynamic compression ratio.
Lower octane and ethanol blend fuels vapourise at lower temp.
Manufacturers warn of engine damage, overheating and vapour lock with lower octane fuels.
Manufacturers warn against using alcohol blend fuel.