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Rpm"s

Started by Lnewman, March 24, 2013, 11:41:19 PM

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Lnewman

Are the recommended rpm"s when running at full throttle the same as the maximum rpm's in the manual?

Stihl 170, 210MS, 290MS, 441MS and Hudson bandsaw

ladylake

 Most stock saws make max power around 9000 to 9600 RPM and should be run there, no screaming and no lugging them down to low.  The 12500 to 14000 RPM in the manual is for tuning them with a tach.   Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

Lnewman

If you are using a tach, then should set at the max in the manual?
Stihl 170, 210MS, 290MS, 441MS and Hudson bandsaw

John Mc

The 12500 to 14000 RPM that Steve mentioned is set with the bar and chain installed, but under no load (i.e. not cutting wood).  You don't want to leave your saw screaming that way for long when tuning, either.  I tend to set mine just a tad richer than the max recommended RPM. For example, if the spec is 13,500, I'll enrichen the mixture till it drops to 13,300.  I figure a little on the rich side won't damage anything, and it gives me a bit of margin for safety if I fill with different fuel, or atmospheric conditions change.

An alternative is to set by ear. Adjust the high speed mixture just rich enough so that the saw just starts to four stroke under no load.  This sound should "clean-up" and do the normal two stroke when under load in the cut.  I don't trust my ear all that much (maybe I'll get better at it one of these days), so I've been using a tach. Lately, I've been trying setting it by ear, then checking with the tach. When I get to where the two seem to match up.

I've also seem some folks use a tach when cutting to check that the saw is tuned for max power RPM under load.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

Al_Smith

I personally know a lot of engine builders ,some of the best in the country .I don't know a one of them that sets a saw engine with a tachometer .Now they might check them with a tach just for posterity but the ear is the final determining factor .Plus obviously how well it cuts .

People have a tendency to take the suggested rpm range as gospel ,like it must run at that speed .Altitude,temperature ,the condition of the saw ,modifications including the muffler render those factory specifications inaccurate in a lot of cases .

Now think about it .Should a saw tuned in Allen county Ohio run at the same speed and power level at approx 900 feet above sea level  as one on a mountain near Vail Colorado at over 9,000 feet altitude ?

T Welsh

As Al mentioned, I tune by ear. I have checked by using a tach later on. I set to be clear running at full throttle and then turn the high speed screw out just a tad to be safe. I also read the plug after a tank full and see how its burning! I was taught the old school way. I have burnt many of 2 strokes down and have now learned my lesson ;D. Tim 

Al_Smith

So far the only saw I ever smoked was by a mistake of straight gassing it .What a sad day that was ,classic 805 McCulloch .One of the last pro grade saws Mac ever made .

On that tuning ,if you are going to err ,err on the side of running rich .A lean set saw doesn't run worth a hoot any ways .All it does is make noise --out of the wood .

HolmenTree

I learned old school, back in the 1970s-early '80s when falling timber 8 hrs a day with the old Jonsereds with solid mount carbs, 621, 80, 801, 90,910,920,630.
We had to carry a carb screwdriver in our pocket and tuning was second nature on the job. The solid mount carbs were prone to vibrating the L / H screws out of set, so us loggers got alot of practice fine tuning our saws.

Then not until around 1982 when I got my first Stihl a 038AV I pretty well didn't have to carry the little screwdriver.
The Stihl with it's rubber intake manifold isolated the vibration from the carb, another thing it isolated was heat which was great for the hot summer days, but not so good on the cold winter days when it's carb was proned to icing up from not getting enough heat.

Tachs? I never owned one. From my old Jonsered days I learned to "set by ear". Fine tuning in timbersport competiton I set my carb with a stop watch in a knot free block of wood.
Making a living with a saw since age 16.

Lnewman

Thanks for all the input, but it's hard to set by ear when you're ear is not yet attuned to doing the setting.   I gather from your comments that it is best to set the high at just a little less than the maximum RPMs -- if 13000 then maybe 12500.   Would everyone agree with that ?
Stihl 170, 210MS, 290MS, 441MS and Hudson bandsaw

John Mc

A little less than the max recommended ON THE RICH SIDE.  If you lean it out past the max RPM, it will eventually drop in RPM as well, but you don't want to run it on the lean side.

I too have not developed my ear to where I trust it. Check out Madsen's tuning directions on their web site.  Click on the "Saw Tuning" link and read that file. It has a great description of the carb tuning process, including an audio file.  Unfortunately, I just don't ear the audio file well enough (poor speakers in my laptop??).  They give you a text description of what they are going to do, then play the audio file of the chainsaw sound. Look for the link that says "Saw Full Rev Adjustment Sound WAV"
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

Caloren

I have listened to that Madsen clip several times and I can't hear the difference either.  :(
Stihl MS 170, Stihl MS 310, Stihl 028 AV Super, and half a dozen other no-accounts! Cat D4 D.

JohnG28

Try a set of headphones. I have listened to that before, its where I picked up some good info.
Stihl MS361, 460 & 200T, Jonsered 490, Jonsereds 90, Husky 350 & 142, Homelite XL and Super XL

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