Tuning a saw by CO levels.

[PatrickIreland]

I have a gas tester which reads CO levels, to set up my cars. Normally set the petrol ones to 1.8-2% CO for best performance.
Is there any way I can use this to set up my saw? Obviously the level would vary with mix, etc., but I fancy the idea of being able to set up the saw using a proper meter, without worrying about listening for four-stroking, etc.
Maybe, get it set up by the (very knowledgeable about old saws) dealer running my usual mix, explain that I want it totally perfect, slip him a couple of notes to spend a bit of time doing it, then measure the levels at idle and WOT as something to aim for?
It's only an old 041, but I like to have all my engines running bang on where they should be. I'm a bit obsessive like that... was going to say "anal", but I know I'd get the piss ripped out of me. Ah well, I've said it now...

 

[willsaw4beer]

Maybe I'm just a nerd but that actually sounds like an interesting tool. Maybe you would start out with a properly tuned saw, then run it a bit rich and a bit lean to get an idea of the variation? Both at idle and WOT. And try it with different saws, and strato saws vs reg saws... Plus try different oils like Stihl, Husky, Sabre, etc...

 

[PatrickIreland]

Not sure if they sell them in the US, but it's just a Gunson Gastester - very accurate if you set them up right (they need 20 mins of "warm-up time", and if you move them that shifts the calibration so you have to wait another 20 minutes) - but during our annual roadworthiness test I have found it to be accurate to within 0.1% when used properly.
I'd just be interested to get a note of the numbers when it's tuned as perfectly as a chainsaw man with 30 years of tuning them can get it, so I can try and replicate that tune when it drifts... given identical mix, etc. each time.

Maybe I'm just a nerd but that actually sounds like an interesting tool. Maybe you would start out with a properly tuned saw, then run it a bit rich and a bit lean to get an idea of the variation? Both at idle and WOT. And try it with different saws, and strato saws vs reg saws... Plus try different oils like Stihl, Husky, Sabre, etc...

 

[ShoerFast]

There is a chance that you would be better off finding the fastest cut (timed cuts in wood at various settings) and matching the WOT RPM's , then resetting for CO2 only ?

Using Co2 % only, would vary with the quality of air (humidity temp and barometric pressure) more then the WOT speed. Watch a tach as you tweek the 'H' settings and you will pick up a trend in your sample by the speed of the engine.

You really need to monitor 4 gasses to get that perfect burn for power, and a timed cut is really the final best judge .

 

[PatrickIreland]

The best power isn't really my goal - just a healthy, nice running saw! The amount of siezed saws I read about on here is huge, and I'd like to know that my CO levels reflected the tune of the saw the way I asked the dealer to tune it - if it would work like that. My gastester just reads CO, I have no tach, and to buy one here costs a lot more than the saw did.
Maybe it's a daft idea which couldn't possibly work, I just thought I'd throw the idea out there.

There is a chance that you would be better off finding the fastest cut (timed cuts in wood at various settings) and matching the WOT RPM's , then resetting for CO2 only ?

Using Co2 % only, would vary with the quality of air (humidity temp and barometric pressure) more then the WOT speed. Watch a tach as you tweek the 'H' settings and you will pick up a trend in your sample by the speed of the engine.

You really need to monitor 4 gasses to get that perfect burn for power, and a timed cut is really the final best judge .

 

[Crofter]

Interesting approach to the old problem!

WOT at no load as Shoer says would not be a good condition to monitor, as too many things (including muffler opening size) can interfere with readings and is not the condition you would want to tune for, which is in the cut conditions. A 4 stroke has the exhaust gas much more isolated from intake variables.

Evaporative cooling / vs fan cooling will be influenced by what rpm you pull it down to and what the duty cycle of loading is. Outside air temperature affects more than just intake air density. This all comes into play and dictates what minimum air / fuel ratio you can run. I am doubtful that you could arrive at an exact best exhaust gas carbon monoxide level. (I know that it is the cats ash for setting up fixed condition combustion processes though).

I think that the leanest condition you could safely select for would be full load continuous cutting for say 5 minutes. Fastest cut times then in 10 or 15 second cuts after the previous heat soaking should be about right, lol! A lot of people would think that was way too rich though.

 

[PatrickIreland]

Thanks, Crofter. So you think my best bet would be just to have "The Man Who Can" set it up for the best (lifespan, not just speed) then run it, and forget the CO meter?
We don't get wild variatons in temps over here, maybe -2c to 25c if I am cutting, otherwise I'll be doing something else - either staying inside with a bottle of bourbon or out messing in the boat, - in my dreams.
In reality it's more like fixing an old generator or installing plumbing in the cabin...
Does anyone think it would be worth a try to read the CO meter at idle, and at WOT in a long, hot cut? A little rich is fine for me - better that than a new piston.

 

[Crofter]

Setting the low speed mixture is relatively safe the old way. Idles for ever, doesnt drag the chain and accellerates willingly. It is the high speed setting that is the challenge and even way more so now that rev limiters are so prevalent. It would be interesting to experiment with the CO meter. I think you would need to get your sample well inside your muffler. A multi cylinder exhaust is not nearly so pulsing and easy to get an undiluted sample from mid stream.

You would have to also be sure that the person giving you the base line reading did indeed know what he was doing. A good big test log should be part of the setup. I sure am not knocking the idea but I have the feeling that sometimes you have to do some of the cooling of a saw by richening the mixture so not sure you could use the same CO levels for all conditions. Two strokes certainly need a richer max power air fuel ratio than a 4 stroke.

I have read with interest a few of "Lakeside 53" posts on the affect of A/F mixture on cylinder head temperatures. I think that is close to the heart of the matter in deciding moment to moment mixture requirements for variable load. You will find lots of thoughts on it on forums that focus on 2 stroke engines in light aircraft use. They would be closer related to a saw, carb wise at least, than auto engines.

If you could come up with a unit the size of a tach. that would give definitely good repeatable carb settings for a saw, I think the world would beat a path to your door!