Proper procedure for adjusting carb with tach

[stihl025]

I did some slight research into the archives and found mixed results. With the addition of a tach on its way from Bailey's, what is the proper procedure for adjusting a carb (after a rebuild) using a tachometer?

Some say adjust by ear, check with tach, but is that really the way it should be done? After reading the saw tune info from Madsen's, I am under the impression that you set the idle speed with the tach first, and then adjust the H screw to its max (or just under max) RPM. The question that I have though, is where does the L screw come into play?

Can someone give me a step by step procedure for using a tach exclusively?

 

[blis]

IMO its best set by ear first, then fine tuning with tach...

 

[West Texas]

The proper adjustment of the "L" jet is what assures you that you can 'start' the saw. If its too lean or too rich either one, you will have difficulty starting the saw, regardless of whether the saw is hot or cold. On most saws you begin with the "L" jet set as indicated on the cover of the saw ( if its a Stihl ).

Start the saw, let it warm up, then set the idle 'low'. Now turn the "L" jet inward or clockwise till the engine starts to stall, note where the screwdriver is located;now crank it out till it starts to stall, then set the jet half way in between these two points. Now using your tach, I set the idle screw to about 2800 to 3000 rpms and it starts when its hot or cold. On the "H" jet, holding it at max throttle, set the "H" jet at the recommended rpms. At that rpm you should hear it "bubble" or "4 cycle". And when you make a trial cut, the engine should 'smooth' out in the cut. Its now ready to work.

Rule of thumb, is its better to have the saw set too rich, than too lean.

 

[Kneejerk Bombas]

Set the jets to the factory recommended setting. If the saw bogs when you hit the throttle, it's too lean, adjust the low speed jet out a little.
If you let the saw idle for 20 seconds, tip it forward quickly, and it changes RPM or stalls, it's too rich, lean it out a little.
Once it's idling properly, set the high speed with a tach.
Why would you adjust it by ear if you have a tach? Although if you don't have a tach, it is possible to adjust it pretty close by ear.

 

[stihl025]

Why would you adjust it by ear if you have a tach? Although if you don't have a tach, it is possible to adjust it pretty close by ear.

Well, that's kind of what my point is... Why would you set the carb by ear if you have a tach? Wouldn't you just exclusively use a tach to set all settings, or am I not understanding something?

 

[ozflea]

Get some-one who knows what their doing the difference between top working revs and disaster is not much if the saw is set too lean, and proves in a very expensive way not to fool with something that you know little about.

This advice is cheap and might save you a lot of hard earned money.

Mc Bob.

 

[stihl025]

Well, I am trying to learn as much as possible from this site, so someday, I can know what I am doing...

Not saying I am going to set my saw at max rpm's as soon as I get my hands on the tach, just trying to understand the methods and reasoning behind the fine art of saw tuning. I will be using the assistance of a tachometer, just want to know how the professionals use them to tune a saw.

 

[Deadman]

Did that $20 tach turn out to be decent, or was it junk?:help:

 

[stihl025]

I am not sure, I had heard and read that the refresh time was a little slow. I decided to buy the SenDec from Bailey's which is reported to be a little slower than Stihl's, but faster than the cheapie. A happy medium in price and performance. Still waiting for it to arrive.

 

[zemmo]

I am not sure, I had heard and read that the refresh time was a little slow. I decided to buy the SenDec from Bailey's which is reported to be a little slower than Stihl's, but faster than the cheapie. A happy medium in price and performance. Still waiting for it to arrive.

I just got an EDT 8 from ebay yesterday, new, for about $90.

 

[Deadman]

I have a Digital Tach on my Quad that I'm gonna try and see if it'll work.
It goes 2 stroke, or 4 stroke, and I think it max's at 20,000 rpm.
Its a Daytone Digital, and its lightening fast. Its almost hard to read because it wants to change so much!

 

[IchWarriorMkII]

I bought the cheap $24 dollar tach, to lean my 353 out to get the E-Tech muffler to run as cool as that hot little ???? will run...


I hope it works well enough to get my 361 in the ball park after it gets broke in, I'd like to get it ripping at full RPM's to see how it cuts... from the few reports I've read its hard to get this saw tuned by ear.

 

[bytehoven]

I just got an EDT 8 from ebay yesterday, new, for about $90.

That was you? I was gonna bid on that tach, but the price was nearing the cost from my Stihl dealer. I'll keep my eyes peeled for when PartsMan posts the next tach at $75 starting bid. :hmm3grin2orange:

 

[THALL10326]

Well, I am trying to learn as much as possible from this site, so someday, I can know what I am doing...

Not saying I am going to set my saw at max rpm's as soon as I get my hands on the tach, just trying to understand the methods and reasoning behind the fine art of saw tuning. I will be using the assistance of a tachometer, just want to know how the professionals use them to tune a saw.

Main purpose of a tach is to insure you do not set the rpm levels beyond the max limit the engine is made to withstand. Thats why all engines have a max rpm rating. If 14,000rpm's is the max, it means 14,000rpm's is the max safe level for that engine. It does not mean it will put out the most power at that rpm, its merely the max you could run it without damage and its cuttng it close at that. Thats where the accuracy of a tach comes in great. The ear can sometime be fooled, the tach is usually on the money and can be relied on for accurate max rpm readings. The tach is also great for setting proper rpms at idle.

Remember too max rpms don't always produce the most power. Many saws cut much better at 13,000-13,300 rpms when they have a max rpm level of 14,000.

Use your new tach to keep your saw within the safe rpm levels it was designed to withstand. Use your log to find that sweet spot where the saw cuts the best. Its ususally always found to be at slightly less than max rpm's. Don't be fooled by MR MAX, he can't fry your engine in a hurry so try to stay away from MR MAX as much as possible, use that new tach to do that..........

 

[zemmo]

That was you? I was gonna bid on that tach, but the price was nearing the cost from my Stihl dealer. I'll keep my eyes peeled for when PartsMan posts the next tach at $75 starting bid. :hmm3grin2orange:

Yep. Small world, huh? It was still a fair bit cheaper than getting it from a dealer, considring the sales tax, and it came to my door. My local dealer probably wouldn't have had one in stock anyway.

 

[Lakeside53]

Well, that's kind of what my point is... Why would you set the carb by ear if you have a tach? Wouldn't you just exclusively use a tach to set all settings, or am I not understanding something?

You need both... not so much to "set" the saw, but to understand what it sounds like when it is running correctly. You wont always have a tach with you, and if your ear is in tune with your tach, you'll know when your saw is heading the wrong way...

Some newer saws, like the 361, are almost impossible to get right just by ear. I set mine with a tach initially, and now my ear knows what it sounds like (and it sounds sweet ), but I have no problem in making a minor adjustments without the tach.

 

[outdoortype]

"Remember too max rpms don't always produce the most power. Many saws cut much better at 13,000-13,300 rpms when they have a max rpm level of 14,000.

Use your new tach to keep your saw within the safe rpm levels it was designed to withstand. Use your log to find that sweet spot where the saw cuts the best."-THall

I agree totally. I played with the adjustments on my saws and found that they cut better when the RPMs below max book specs. But the tach will tell if your in the safe zone. I like the Fast Tach from Design Technology. It memorizes max rpm and I don't have to remove the cylinder cover.

And by the way THall, I followed your advice on tuning the 025 and it worked great. I like carb adjustment on that saw-no mushy feeling limiter caps. Are the newer Stihls like that?

 

[bytehoven]

Yep. Small world, huh? It was still a fair bit cheaper than getting it from a dealer, considring the sales tax, and it came to my door. My local dealer probably wouldn't have had one in stock anyway.

Well, congrats on the new toy.

I have been thinking of starting a thread about renting/sharing a tach? So I'll ask you if you would ever consider shipping your EDT 8 to someone for a brief period ( 1 week) so they could tune their saws?

If yes, the next logical point of discussion would be "quantos deneros?" :hmm3grin2orange:

If it's an idea that might have legs, I would be willing to start a thread.

 

[West Texas]

The tach is a great tool; but, when adjusting the "L" jet, there is an 'interaction' between the 'Idle' screw and the 'L' jet. You can get the recommended rpm at idle speed by adjusting the idle; and, have the wrong or too lean setting on the 'L' jet. That's why I recommended the setting procedure I did for setting the "L" jet, with the idle at low speed. Once the "L" jet is set for optimum starting, then you can take the tach and the idle adjustment to get the recommended 'idle' rpm and have a saw that will start when its cold and not stop when it gets hot. On the "H" jet, I have both of my 361's, which are 'woods' modified, set below the suggested rpm; but, I've done this by turning the "H" jet out, making it richer. I get a discernible 'bubble' or '4 cycle sound' at max throttle, that smooths out in the cut. I can push down quite hard on the saw when its in the cut and it holds the rpms constant, using this adjustment procedure. I use the Stihl tach and I use my ear and I listen to my saw in the cut and I 'know' the feel when its cutting and performing at its best. All of the above comes with working with your saw, the tools and the conditions under which you will be using the saw. Good luck. We all started at ground zero and learned as we went.

 

[stihl025]

The proper adjustment of the "L" jet is what assures you that you can 'start' the saw. If its too lean or too rich either one, you will have difficulty starting the saw, regardless of whether the saw is hot or cold. On most saws you begin with the "L" jet set as indicated on the cover of the saw ( if its a Stihl ).

Start the saw, let it warm up, then set the idle 'low'. Now turn the "L" jet inward or clockwise till the engine starts to stall, note where the screwdriver is located;now crank it out till it starts to stall, then set the jet half way in between these two points. Now using your tach, I set the idle screw to about 2800 to 3000 rpms and it starts when its hot or cold. On the "H" jet, holding it at max throttle, set the "H" jet at the recommended rpms. At that rpm you should hear it "bubble" or "4 cycle". And when you make a trial cut, the engine should 'smooth' out in the cut. Its now ready to work.

Rule of thumb, is its better to have the saw set too rich, than too lean.

Think I may have something wrong. Got the tach today, reset all of my carb setting to factory (1 turn out) to start out fresh. When I tried to set the L setting as above, turning the L jet inward or clockwise, the engine gained RPM's and never stalled... I could seat the L jet all the way down. Now when I backed it out past the 1 turn mark, I could make it stall as described. Is that normal? I referred back to the Madsen's instructions that I had printed and my saw is doing exactly opposite as they say it should. ??? Help.