Chainsaws & Size (probably again)

[Leo Van Der Loo]

It has nothing at all with the time to produce a spark. It has to do with the time it takes for the fuel to build up a sufficient pressure once ignited by the spark. At very high RPM's the spark may occur as much as twenty degrees before the piston reaches TDC in order to have mostly complete combustion by the time that the exhaust port is opened.

Sorry I do agree with you Bill on the timing issue, and about the Octane rating, as you saw I assume, the higher octane is for being able to withstand higher compression before combustion.

I should add that my thinking on the spark time taking, was from the time the field was collapsed on the coil, and the time it takes to get to the spark plug points, of course that was wrong, as the actual sparking is what is used for the timing 😳.

 

[olaf Vogel]

Octane rating can be increased by a number of different oxidizers such as methanol, ethanol, propanol, and f-butanol. Drag racers used nitromethane. There were some other additives that were extremely toxic.

Not sure if it increases octane rating. But back when I used to modify cars, especially high pressure turbos, one great solution was "water injection".
At 14 psi of boost, a solenoid would open, and a mixture of distilled water was squirted in. It lower the EGTs dramatically and allowed for a bit more aggressive timing. You just had to watch that you didnt run out of water. 🙂

When this old saw was running rough, I have used octane booster before with success.
Now that its been rebuilt, its much smoother.

I'm sure that there must be a special place in the hereafter for folks who borrow tools. 🙄 You have to ask yourself why they want to borrow your tools. The reasons that come to mind aren't very comforting:

• They broke their tool and want to break yours as well.

Yeah, he's good guy who has done me lots of favours, and as a landscaper i figured he knew his way around 2 strokes.
Now he owes me a few more favours.....

BTW - I got the parts of Baileys Online. These were aftermarket since the saw is 30 years old and Stihl doesn't have any NOS parts.
But prices were excellent, so was service. Can highly recommend them!

Haven't tried the Huskys, but all my Stihl saws have been excellent.

 

[Bill Boehme]

Not sure if it increases octane rating. But back when I used to modify cars, especially high pressure turbos, one great solution was "water injection".

It doesn't increase octane rating, but it does provide benefits in certain circumstances. Water has a high heat of vaporization so it cools the intake as well as cylinder head temperature. This allows an engine to have a higher compression ratio without detonation. Also, the cooler intake temperature means that the gas/air mixture will be denser so that also helps to increase power. On the negative side, the water vapor means that the oxygen intake is reduced a bit which counteracts some of the power gained from having a high compression ratio. So the benefit is limited to special situations such as a high compression engine with a turbocharger or turbo supercharger. Despite the claims made in the J.C. Whitney catalog, water injection doesn't improve the performance of an unmodified stock engine.

 

[Michael Schneider]

Piston driven airplanes burn high octane and can't have ethanol. If you have a small airport around, you might be able to by gas there. Someone said that boat marinas also sell gas without ethanol, as many boats do not do well with ethanol mixes. Any other standard places to buy ethanol free gas?

 

[Bill Boehme]

Piston driven airplanes burn high octane and can't have ethanol. If you have a small airport around, you might be able to by gas there. Someone said that boat marinas also sell gas without ethanol, as many boats do not do well with ethanol mixes. Any other standard places to buy ethanol free gas?

While it's true that currently manufactured aircraft engines are designed to burn 100LL avgas (100 octane low lead) there are many aircraft engines that run on 80 octane avgas. The concern many years ago about ethanol was the potential for vapor lock at high density altitude causing fuel starvation. However, testing has not shown this to be a problem in gravity fed systems as well as some fuel pump systems. The engine in the Cessna Skylane that I owned originally was designed to burn 80 octane avgas, but it has an STC (supplemental type certificate) to use 87 octane auto gas with an ethanol content of 10% or less.

For chainsaws there's no reason to use leaded gas. The 100LL avgas, despite the low lead moniker, has four times as much lead as standard leaded auto gas had. If you want to foul the plug in your chainsaw then using leaded gas would be a good way to do it. Besides, chainsaws are designed to run on auto gas with ethanol so it doesn't make much sense to buy super expensive avgas for no benefit in performance. By law, avgas can only be dispensed to fuel aircraft.

 

[Zach LaPerriere]

Piston driven airplanes burn high octane and can't have ethanol. If you have a small airport around, you might be able to by gas there. Someone said that boat marinas also sell gas without ethanol, as many boats do not do well with ethanol mixes. Any other standard places to buy ethanol free gas?

Michael, My understanding (though I am only passing on what I have heard) is that federal law mandates 10% ethanol at all regular fuel pumps except by exception. I live in a SE Alaska where it is a temperate rainforest and quite moist, and we do not have ethanol in our gas because ethanol and moisture apparently don't go together well in fuel tanks.

Many marine gases do in fact have ethanol...you'd just have to check. Some specialty gas stations sell fuel without ethanol for older vehicles, as is the case near where my cousin lives in Colorado and a station that specializes in vintage vehicles.

Bill, my understand is that ethanol is terrible for all seals and hoses, especially the smaller ones in chainsaws. I've talked with guys who have to change their fuel lines every 6-12 months in their saws in the contiguous 48 states. By contrast, my dad recently gifted me his Stihl 041AV that has the original fuel lines: nearly fifty years old and going strong.

 

[Bill Boehme]

Bill, my understand is that ethanol is terrible for all seals and hoses, especially the smaller ones in chainsaws. I've talked with guys who have to change their fuel lines every 6-12 months in their saws in the contiguous 48 states. By contrast, my dad recently gifted me his Stihl 041AV that has the original fuel lines: nearly fifty years old and going strong.

That's a really old concern that may have been true many decades ago. with some older types of rubber, but ethanol has been used in gas for a very long time now and deterioration of seals and hoses due to ethanol Is no longer the case. My 30+ year old Sthil chainsaw has only ever used gas with ethanol and hasn't ever needed any maintenance except for replacing the spark plug every couple years and replacing the foam air filter every five or six years. Before that I had a Craftsman saw and the fuel hose was always getting brittle and cracking ... and I believe that I used leaded gas in it. Quality of materials used rather than fuel might be the answer to why they are having problems.

 

[Leo Van Der Loo]

I believe my brother was using regular airplane gas in his airplanes that he build, he had Lycoming engines in them, though this is already quite a few years ago, as he had to quit flying when he didn’t pas his medical.
Turned out he had a tumor in his inner ear, got it treated in Sweden, where they used the Gamma knife procedure, he is still with us and will turn 91 in Sept. God willing.

 

[Gerald Lawrence]

ok so today I checked the book on my new Stihl MS 250 and you guessed says to use 89 octane and up to 10 % alcohol is ok. Live and learn. Thanks for the info from everyone I have learned some things on this one.