Taching a saw

[TexasTimbers]

I quit fooling around with those $25 cheapo POJs and got the TT 20K by Design Technologies. I love it. I think. What I mean is, while the saw is WOT or in the cut this wireless model (which also allows the use of leads, which are provided)  updates so fast you never see a steady reading. So am I supposed to use the "Max RPM" reading that the saw achieves or am I suppsed to try and average out all those readings as they falsh in front of my eyes?  :P

This thing is easy to use and the wireless capability makes it easy to hold it in one hand while burying the blade to get your reading, I just don't know what reading to use, because they numbers I am seeing flashing before my eyes are usually alot lower than what the max RPM number is when you hit the Max RPM recall button.

[sawguy21]

I would go with the max reading. I use the Stihl EDT6 wireless digital and find it very easy to use. Sometimes the readings bounce around for a bit but settle down to within a 100 rpm if I wait.

[TexasTimbers]

Maybe I should try using the wire and see if it quits jumping. i have not used it enough to say the wireless function does not work well. I better use it some more. Shucks. That means i have to use my chainsaws some more. Oh dern.

[Ed]

The recommended condition is to set the max speed at no load, just a bar & chain on the saw. Not in the cut.
I set mine while running the shortest bar and chain combo for that particular saw. If you set it max with a 50" bar, then put a 24" on the saw, it will be running way over the max rpm.
I will take a saw a little over the limit but I don't push my luck. With a modded saw you can run it higher..........how much? I don't know and won't guess.
Also make sure your saw doesn't have a rev limiter before trying to crank the rpm way up.

Ed

[Cut4fun]

I use a EDT-5 refresh at .5 sec and also have the cheapie $24 tach refresh at 2.5 secs. You shouldn't have any jumping numbers wireless or with lead attached.
Heck my cheapie tach dont even jump at max.

[thecfarm]

That's how the saw guy does the tach on my saw,wide open,no load.

[Al_Smith]

 A tachometer is indeed a nice tool but don't bet your life on it.The speed outside the cut means little more than noise.The speed in the cut is what counts.

A saw that 4 cycles at 12 thou and holds the cut at 10,500 means a lot more than a screamer of 14 thou that  dribbles down to 8 thou in the cut.

[TexasTimbers]

The speed outside the cut means little more than noise.The speed in the cut is what counts.

This is what I believe too. I don't have all the experience to explain why, it just makes more sense to me. Chainssaws spend their lives on the playing field not sitting on the bench screaming rah rah. I want to know what they do on the court.

[joe_indi]

kevjay,

To get an accurate reading its better to use the wire.

To set the maximum speed , out of the cut with the bar and chain fitted, first set both the screws to standard setting, usually one turn out from stop, it is 1 1/4 turn out if the saw is a Husky.
Depress the throttle just enough to get a speed  above fast idle, sort of progression point above fast idle.If the engine 4 strokes, close down the L screw slightly so that the 4 stroking is reduced (not completely eliminated)
Now the engine will have a very fast idle even with your hands off the throttle.
Use the tach to fine adjust  the L and Idle screw to get the idle speed as per the specs.. You will need to adjust further to get a finer setting.

Now rev up to full throttle and get the reading.From here you have a few choices.You could adjust the maximum rev to company specifications.
I  do it a bit differently.I close down the H screw to get the maximum RPM and then turn the H screw out so that the RPM drops by 1000 or 1500.
1000 is okay if you are cutting smaller stuff, but 1500 is safer if you are cutting bigger logs.

If your tach is similar to the Stihl EDT, make sure the setting is for 2 stroke single cylinder, or you might get some strange readings.

Joe

[dnalley]

I won't know if I don't ask, But what is meant by 4-stroking?  I also saw this in an old Husky owner's manual telling how to adjust the H and L screws.  Sorry for my ignorance, but this I don't quite understand.  Thanks, Dwight

[sawguy21]

Four stroking is the sound it makes when slightly over rich. The rpm's drop slightly, pick up and drop again. This is necessary under no load conditions so the saw is running rich enough under load to provide maximum power and not overheat.

[jokers]

kevjay,

To get an accurate reading its better to use the wire.

To set the maximum speed , out of the cut with the bar and chain fitted, first set both the screws to standard setting, usually one turn out from stop, it is 1 1/4 turn out if the saw is a Husky.
Depress the throttle just enough to get a speed  above fast idle, sort of progression point above fast idle.If the engine 4 strokes, close down the L screw slightly so that the 4 stroking is reduced (not completely eliminated)
Now the engine will have a very fast idle even with your hands off the throttle.
Use the tach to fine adjust  the L and Idle screw to get the idle speed as per the specs.. You will need to adjust further to get a finer setting.

Now rev up to full throttle and get the reading.From here you have a few choices.You could adjust the maximum rev to company specifications.
I  do it a bit differently.I close down the H screw to get the maximum RPM and then turn the H screw out so that the RPM drops by 1000 or 1500.
1000 is okay if you are cutting smaller stuff, but 1500 is safer if you are cutting bigger logs.

If your tach is similar to the Stihl EDT, make sure the setting is for 2 stroke single cylinder, or you might get some strange readings.

Joe

Joe, I don`t see any benefit in adjusting the low the way that you suggest and adjusting the high speed by your method can be downright injurious to the saw. I`ve seen many pro saws that will rev 16-17,000 rpms free speed so by your method I would richen the mixture to get no load speed down to maybe 15,500 for big wood? That is more than likely dangerously lean, reducing power and increasing wear and the risk of seizure.

The way that Kevjay and Al, just to name a couple, have suggested of adjusting for max rpm in the cut is the best. Adjusting for factory spec is safe for those who don`t want to adjust in the cut.

[joe_indi]

jokers,
It is important that you correctly adjust the low screw first precisely for the reason you mentioned about the maximum rpm climbing to 15000 - 17000.
The setting of the low screw does have an small effect on your high speed.It becomes more critical when the saw is at full throttle.A portion of the fuel is supplied by the low speed circuit.
So if you set the high screw first and then adjust the low(read lean out) your pre-set high becomes lean.
If I get a 'Screamer' (a saw which revs more than the usual specs),before any further adjustments on the carb,I would check the saw for leaks both under pressure and under vacuum. I would also check the the carb metering settings.If it still screams I would set the high speed by ear...........a bit of 4 stroking with bar and chain fitted , out of the cut.

[jokers]

Joe,

I know all about how the lo speed fuel circuit delivers approximately 33% of the high speed fuel and why it is important to set the lo speed first, I just don`t follow the logic in your prescribed method.

I have seen many saws in perfect condition that will free rev far above the factory spec and that is what makes the first instruction that you gave us deficient. The additional info that you included in your most recent reply to me where you mentioned adjusting by ear fills in a blank but had I not questioned your stated technique would you have added that info? We all do it on occassion but incomplete info is often just as bad as incorrect info.

[joe_indi]

Jokers,
My apologies for having left out the 'tuning by ear' bit out of my first reply.But I thought that, that method was too common  to mention.
You need also to know that we in India have a more common problem with saws that is related to fuel.
The saws that we get here, especially the Stihl ones are actually made for the western market.Due to  stringent  emission norms of your countries, the saws are now designed for your fuels.
For example the MS460 has a fixed jet of 0.68 compared to the 0.70 in a 046.
Limiter caps restrict what you do to carb settings.
If I am not mistaken the crank too has been modified so that the ignition timing is slightly advanced.
This is not good news for us in a country where the octane rating is claimed to be 86, but never comes close to 80 due to fuel adultration.
Add a higher tropical ambient temperature, which is in the range of 32 to 36 deg C and rising gradually due to global warming(2 deg at the last count).You dont have the ideal exactly yconditions for a saw more suited for moderate climates and 90+ RON fuel .
In the pre-MS era it was possible to get the saws to run on above-specs rpm.But now  what I actually do is try to downgrade the performance so that the engine does not blow.
Bigger jetting, retarding the timing, replacing the present L and H screws with the older types,  adding another cylinder gasket to decrease the compression are some of the remedies I resort to to get the saws working with our fuels in our climate.
So if my info was incomplete, you will have to forgive me because the omission was not deliberate but because such obvious things do slip from ones mind when one does not do some things anymore.

[konrad695]

kevjay,
I have the same tach.  I bought it when I started messing around with mufflers.  You can pick your own way to tune a saw.  I wanted a tach to "ballpark" my saw before I tuned it by ear.  The problem was "my tach was bad."  Try it on something else.  I too had the RPM's going all over the place.  I used it on a car, van, 3 saws, a lawn tractor, and a generator.  Readings went up and down with the wire lead being useless.   If this is your problem contact Design Tech.  They were very helpfull to me and sent me a new tach in a short time.  It also turned out that the new tach read about 10% lower than the first, which put all engines in the ballpark of manufacture specs.  With the new tach. everything became easy.  Hope you have an easy fix to your problem.
Konrad

[Simonian]

I tune by ear After adjusting the low jet first to get good idle and good acceleration off idle with no hesitation, I then turn the High needle till I get a good 4 cycle. Then start leaning tell it just starts to 2 cycle. If I think I went too lean , I back it out to catch the 4 cycle then back again to that sweet spot. If the saw gives you problem with this, it has an air leak that needs to be fixed as this makes it impossible to get low and high jets set correctly.
I believe each saw has it own tuning point and the only way to find it is by ear.
I once had a Dolmar 420 and at that time was using a tach. The problem was that it peg the tach at 15k but the saw would not cut worth a darn because it was still too rich. I took it to the sweet spot by ear and it ran cut great for many years. I still do not know why I sold it

[sawguy21]

Your system works great on older saws and is what I am used to. However, a number of current models have rev limiters built into the ignition and they will 4 cycle if run too lean. A tach is critical with them.

[Simonian]

That may be so on some new saws But doing it by ear still should still work. If done with caution it is not possible to run it too lean. Thus avoiding over revving and kicking in the gov. I think the Husqvarn 359 has a rev limiter on it and it works on that saw

[TexasTimbers]

. . . . . if done with caution it is not possible to run it too lean. . . . .

I don't know much about taching saws but I know caution or not, anything is possible with men and machines, good or bad. I'll stick with the tach.

[Simonian]

I am not saying anything bad about using a tach but it is a tool to help you learn to find that sweet spot by ear. Once you know and feel that spot you will not need to rely on the tach as much as you do now.
The more you know the less you need is my saying.

[TexasTimbers]

Cool. But I am a chainsaw tuning dummy and don't wanna learn the hard way. That's all I'm saying. Guys like me have to take our saws to guys like you unless we have tachs. ;D