running saws rich

[simonmeridew]

What's the major problem with running the high speed a little rich? I run my 034's so that if I let off a little in a cut they burble a bit, but stop and even out when I start cutting hard again. Am I looking at carbon on the piston, a loaded up spark plug, or nothing bad. The saws( 3 of them) all run great, maybe a little slow ( 5-10 pulls) cold starting, but idle and run great.
simonmeridew

[sawguy21]

 ??? Sounds like the perfect setting to me.

[chucker]

  you wont burn them up thats for sure! first problem might be a fouled plug , but their cheap compared to a scored /burnt piston.... seals seem to last forever as well....  go for it in my book!

[Left Coast Chris]

Another thing to watch out for is a oil pluged screen on the mufler.  Just a little resistance on the mufler screen and the saw will not run right.   At least that is what my old Husky would do.

[Cut4fun]

I run my 034's so that if I let off a little in a cut they burble a bit, but stop and even out when I start cutting hard again.

You mean a little like this 166 is too  ;)  I think about everyone that is cutting hardwood firewood is set up about like that too.

http://www.youtube.com/watch?v=YqXOHsQE3Wk

[John R]

What is it with all this THIN firewood?   :D

I always run my saws rich, I mix a one gallon bottle of oil with about .8 of a gallon of gas.
Never had any problems doing this, and it makes me feel good.

[tlandrum]

you want a saw to 4 stroke a little out of the wood but i dont like onr too rich . i have built way to many for people becouse of carbon scoring

[Cut4fun]

What is it with all this THIN firewood?   :D

Not firewood, thats bonfire chips  :D. 

It's called testing and tuning saws after rebuilds, carb work etc. I keep wood on hand in the clean debarked version to test different good chains too  ;). 

[simonmeridew]

yes, Cut4fun, that's almost exactly what it sounds like, you let off a little during the cut and you get a little tongue-waggle sound, then you dig in again and the work sound begins again.
simonmeridew

[John Mc]

I always run my saws rich, I mix a one gallon bottle of oil with about .8 of a gallon of gas.
Never had any problems doing this, and it makes me feel good.

The references to "rich" here were mostly referring to carb adjustments, not how much oil is in your fuel mix. BTW... more oil in your mix will make your saw run a bit leaner.

[sharkey]

>>BTW... more oil in your mix will make your saw run a bit leaner.<<

I could never understand the reasoning on this?  I do understand the volumetric measurement of whatever mix ratio is being run such as 32:1 or 50:1 and so meaning that the 32:1 mix has 3% oil and the 50:1 has 2%.  Are you suggesting that because the 32:1 mix has more oil in the fuel that the engine is burning less fuel?   

I dont buy it because as soon as the induction fuel mix hits the warm metal of the crankcase, the fuel evaporates and the oil falls out of suspension.  For what its worth, the crankcase has a compression ratio too, and on most saw engines the ratio is 1.5:1.  Because of the crankcase compression ratio the amount of fuel reaching the combustion chamber is basically unchanged from mix ratios of 16:1 through 50:1.     

I run all my two strokes at 32:1 and a little bit rich on the top end.  Most of the carbon that accumulates in the cylinder is from unburned gasoline not oil.  A little extra oil is good insurance against differences in barometric pressure and alcohol laced gasoline.  Besides the extra oil floats the carbon out of the cylinder and keeps the insides cleaner.  Maybe Im wrong but this is what I see.

   

[ladylake]

I'd think more oil will make it run leaner due to a higher viscosity makeing it harder for the mix to get through the jets.   Steve

[John Mc]

As Steve already mentioned, the main reason that more oil makes the saw run leaner is that it changes the viscosity of the fuel mix, affecting how it flows through the carb. This is not to say that you can't adjust for it (at least within the variations of mixtures we're talking about here). A tweak to the carb's mixture setting, and you can easily counter the effect. If you're mixture settings are optimized for 50:1 mix, and you switch to 32:1 without adjusting the carb, you will be running a bit leaner. This is why it's important to adjust the carb to the type of fuel, and the amount of mix oil you will be using.

A good saw shop knows this, some may ask you to bring your saw in with the fuel you are using if they are going to be adjusting the carb. Alternatively, they will ask what you are running, and/or set it up to run a tad rich, figuring that running a bit on the rich side has much less of a chance of doing damage. This gives you a bit of a buffer, if you run a different mix than what they set the saw up on.

I've heard another factor as a possible secondary reason why going heavier on the oil makes for a leaner running saw (unless carb is adjusted): Supposedly, the carb allows a certain volume of fuel mix through (other things, such as viscosity, being equal). The more of that volume is oil, the less is fuel, resulting in a leaner running saw. I haven't thought about this much yet, but it seems to make some sense.

John Mc

[John Mc]

While we're on the subject of rich vs lean...

One other factor, unrelated to oil mix: running ethanol blended fuels vs "pure" gas will affect how lean your saw is running. (E10, a 10% ethanol blend is about all I can get around here any more.) The stochiometric ratio is the point where (theoretically) all the fuel mixes with just enough air to for the fuel to completely combust. For pure gas the ratio is about 14.7 to 1 (mass of air to mass of fuel). Ethanol is about 9 to 1. Ethanol is "looking" for less oxygen than gas is... ethanol is an oxygenate - it has more oxygen already in it than gas does. Ethanol and all the other additives in E10 gas bring the ratio down closer to 14 to 1.

In practice, most engines run under any significant load are set up to run richer than the stochiometric ratio - otherwise they'd run too hot. The relative proportions hold true, however. So if you set your saw up for running straight gas, and switch to E10 without adjusting the carb, you may well be running leaner (depending on what other additives were in the "straight gas").

If you set up a tad rich with straight gas, you've got a little buffer. You might be OK with a switch to E10. If you were set right at the peak for straight gas, you may cause problems if you switch to E10 without adjusting the mixture. I suspect that some of the saws that "burnt up from running ethanol gas" were actually due to failure to readjust the mixture when the operator switched from straight gas to E10. (Though ethanol does have plenty of problems even if you do adjust the mixture appropriately for it.)

John Mc

[ladylake]

Right  My BIL bought a new saw that ran fine with my 91 oct gas without ethonal, next time out I'm listing to he cut, sounded lean, it was with his ethonal gas. I had to pull the caps and adjust richer. After that I got him to spend the extra money for the ethonal free gas.  He might use 3 gallons a year so it won't break him.   Steve

[John Mc]

You are lucky you still have the option for ethanol free gas. All of my sources around here have dried up within the last month or so. They just can't get it. Even the distributor, who had a single pump beside his office, doesn't have it anymore. I'm halfway through my last 5 gallon can right now.

[Mad Professor]

You are lucky you still have the option for ethanol free gas. All of my sources around here have dried up within the last month or so. They just can't get it. Even the distributor, who had a single pump beside his office, doesn't have it anymore. I'm halfway through my last 5 gallon can right now.

Try a marina, or 100LL at the airport

[John Mc]

Try a marina, or 100LL at the airport

I've actually posted that advice myself here a few times. The nearby marinas got their last shipment of ethanol free in Sept 2010.

I'm a pilot, and have access to 100LL, but I will not burn it in my chainsaw. Having worked for a company that heat treats steel in molten lead, I've heard plenty about the dangers of lead. I don't relish the thought of a chainsaw spouting out the exhaust from tetraethyl lead laced fuel a couple of feet from my face. Especially since 100LL has about 3 times the lead of the old leaded auto gas.