OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters What unleaded fuel is best for a 2 Stroke motor?

I have been using Unleaded 91 RON as the base for the 2 stroke mix for a long time for a Black 'n Decker bent shaft trimmer, a Stihl straight shaft 2 stroke trimmer and a Ryobi blower vac.
I also use it in the 4 Stroke Honda lawn Mower.

Recently the Stihl was in for repair and the mechanic was making a case for only using Premium Unleaded RON 95 as the base for the 2 stroke mix? As any one heard this before? I have looked and i can see nothing written about this.

Its because a lot of standard unleaded has ethanol in it now whether the pump says it or not.

To put things in perspective today I looked at an old victa I got as a trade in on wednesday, I noticed the old fuel line was worse for wear so I replaced it, the fuel in the tank was new so I left it in there. Within 6 hours the ethanol fuel that was in the tank had started to melt the brand new victa fuel line I put on, I dumped that fuel quick smart and refuelled. Not only did it run better it hasnt attacked the second new peice of fuel line again.

Hey ABC,

Yep I'd go with the Stihl tech on that one.

Personally I prefer to use BP Ultimate with synthetic oil for all my two bangers. Generally you dont use much fuel anyway so the extra cost for the "best" you can buy is a non-argument really. My Stihl 098? ran best Stihl lube and brand name Prem 98 fuel (non ethanol) until someone stole it anyway

Cheers

Definately The higher Octane.Setting aside Joes post for 1 min...The higher the rating the cleaner the burn.Since a two stroke has oil as well to consider in the combustion process it needs to be burnt more efficiently.The low octane fuels tend to foul and build up carbon much more quickly.There are cases for and against.Most GOOD manufacturers design their engines to run on certain fuel types and ratios.When the introduction of unleaded crossed over many years back the fuel octane for "Super" was also around 95 octane and the prefered choice by mower makers.
Now back to what joe was saying.This is true..So VERY true...A few years back when the big hoo ha was on about dishonest fuel sellers putting Ethanol in their fuel their was no screening.Its not as simple as just adding ethanol to fuel..It has to have additives one being ANTI moisture agents.In a 12 month period I saw a massive increase in failing fuel systems,severely rusted tanks totally corroded and rusted fuel line and injector rails.Whole systems that were destroyed completely by the use of shall we say unlicensed ETHANOL...Now things are different and car manufacturers cater for the use of ethanol much better.But the people were burned already.This is in my opinion why ethanol still isnt trusted completely.I do not know if mower manufacturers have recommended the use of ethanol fuels,so in Joes case maybee they didnt factor in the damage it could do to other components and why his fuel line melted:)

Blue, I do not understand your basis for saying "The higher the (octane) rating the cleaner the burn". I do not see any reason why this should be so. Octane rating measures resistance to detonation - if higher octane fuel burned cleaner in an engine that did not require that octane level, it would be by accident, simply because some of the octane improver additives and/or cracked or hydroformed hydrocarbons happened to have that characteristic inadvertently. From what I have read octane improvers, in particular, are more likely to make the burn less clean.

With regard to low octane fuels tending to increase fouling, that appears to have been true back in the days of very low grade petrol being raised to high octane by the use of large amounts of tetra ethyl lead, but those days are long gone. Large amounts of octane improvers may cause fouling, but it seems unlikely there will be larger amounts of octane improvers in low octane fuel, than in high octane fuel.

I generally agree with your warnings about ethanol, which tends to be unfriendly to fuel system polymers, and hygroscopic as well. The absorbed moisture causes fuel system corrosion, fuel discolouration, and ultimately may cause the fuel to become non-homogeneous.

i only use caltex vortex 98 in everything car, boat, bike, mowers and anything else i get hold of [except the work van i only use vortex diesel in that]

i have never had any fuel related problems in anything using vortex fuels

i dont see the point in saving a couple dollars in poor fuel

just on a side note ethanol fuel would have to be around 40 cents a litre cheaper then premium to actually work out cheaper in most cars

Sounds all good Grumpy,straight from the text book,I stand corrected.Somethings misalign over time.Most people I know are and have been under the assumption that this was the case.Ive been a mechanic for over 20 years and its something you just know/think you know.Its not something Ive delved deeply into.The manufacturers,drivers,race car drivers and the like would all dispute this.BUT upon reading further It is a case of use whatever octane rating your machine was designed for.High compression or low compression systems will dictate what fuel you use.Thankyou grumpy for clarifying something I thought I knew:)
As for the Ethanol yes I guess for this one its a case of I had no choice but to investigate and educate myself in order to fix the problems the Ethanol caused in these cars.
The question still has not been answered though...Why did the Stihl tech tell ABC to use 95 octane?Is this the fuel recommended by Stihl for its engines?And what is the basis for the other two members use of High octane fuel???

German cars are designed for 95 octane, and it would not surprise me if Stihl followed the same line of thinking. In the case of cars it is somewhat rational: the additional energy used in producing the higher octane fuel can be recouped in the better fuel economy it delivers if you have developed the car's engine to require the higher octane. This mostly means you can raise the compression ratio to the limits allowed by 95 octane instead of 91, and the higher compression ratio improves your fuel economy. When you trade off the higher fuel economy achieved in the car, against the additional energy consumed in the oil refinery (or the additional octane improvers added to the fuel), you can at least break even if everyone does their part correctly. The practical difficulty is that outside Europe, most fuel is 91 octane, and if you detune a 95 octane car for 91 octane fuel without reducing the compression ratio, the fuel economy penalty is fairly severe (you have to do it by retarding the ignition).

So, my guess would be that if Stihl recommends 95 octane (and I doubt they do) it would be a sort of German cultural thing, not for any more sensible reason. Globally, most of their customers would be using 91 octane fuel, and they would be most unwise to design the engines for 95 octane. However from what ABC1 said, it sounds as if the recommendation came from a local service mechanic, not Stihl. The mechanic may have been concerned about the possibility that 91 octane fuel might contain ethanol, as Joe said. If that was not the reason, my guess would be that he/she simply passed on some kind of street thinking that was not based on reality.

Joe, I understand that ethanol is a solvent and that is why i will not touch E10 at all but to be clear i was speaking about standard unleaded petrol 91 RON...are you saying the standard unleaded 91 from a petrol bowser can be fouled with ethanol ?

I am just saying that some servos arent as honest as they should be all bar one place in town here the fuel smells watered down and very "ethanoly"