Chainsaw Carburetor Tuning 101

[MasterMech]

Question for ya Mech - will the spline tool for a MS 290 (I know I'd have to fool with the tabs to get to it) be the same one as a Husky 350?

AFAIK - The MS290 uses a standard flat-head screwdriver for carb adjustments. The only tool required may be the one used to remove the limiter caps on the carb.

 

[MasterMech]

I FOUND THIS ADVICE
It seems to work well without a tach. But, what do I know, I am just a cowboy with a bag of tools.
This is routine operator maintenance.
1. Start your saw and run it for a few minutes to warm it up.
2. Set your saw down, let it idle for 30 seconds, and then pick it up and tip it forward (handle up and bar down).

The saw should run upright, upside down, standing on-end, or lying on its side equally well. Letting it idle for 30 seconds doesn't really do anything for it either. If the saw stalls or changes rpm when it changes position, the crankshaft bearings/seals are most likely worn and/or leaking and should be replaced. Pressure/vacuum test to confirm.

3. If it keeps running, go to Step 4. If it stalls, tighten the Low Speed screw. This will reduce the amount of fuel entering the carburetor. Repeat Step 2 as necessary.

No it won't. The L screw only affects the amount of fuel delivered with the throttle closed or partially open.

4. Rev (accelerate) the idling saw.
5. If it accelerates fine, go to Step 6. If it “dogs,” loosen the Low Speed screw. This will increase the amount of fuel entering the carburetor. Repeat Step 4 as necessary.

Again, incorrect. The inlet needle valve and the diaphragm control fuel flow into the carburetor. This happens automatically and requires no routine adjustment from the operator.

6. Rev the idling saw for about 5 seconds (never rev it for 10 seconds or longer).
7. If it “flutters” while being revved, this is good, so go on to Step 8. If it “screams” while being revved, this is bad. Loosen the High Speed screw. Repeat Step 6 as necessary.
8. If the chain is stationary while the saw idles, you’re finished.
9. If the chain rotates around the bar while the saw is idling, adjust the Idler Screw as necessary to make it stop. This situation can be fixed in a matter of seconds and is extremely dangerous if not corrected.

When setting the final idle rpm's, the L screw is generally set quite rich to prevent the saw from leaning out excessively on decelleration. This is what I'm doing in the video at aprox the 02:10 mark. The L and LA settings should be finalized before moving on to the H setting because the L setting will affect the H setting but not vice-versa.

That’s it. Less than five minutes of your time can make a big difference in how well your saw runs. Two additional tips are 1) use hot water and dish soap to clean a paper-type air filter (let it dry before using), and 2) use chainsaw gas to clean a wire-type air filter (you don’t need to let it dry before using).
This information will help your saw run more effectively and efficiently.

I totally agree with cleaning the air filter and the muffler screen. Should be done before you begin tuning. Also, you should reset to factory default carb settings (if known) before getting started.

 

[HDRock]

Also, you should reset to factory default carb settings (if known) before getting started.

The only factory default settings I can find for the 445 are
Maximum power speed – 9600 RPM
Maximum recommended engine speed – 13,000 RPM
Idle speed – 2700 RPM
If I had a tach , would I be trying to set the high RPM 9600 and not exceed 13,000 ? If not, What do they mean by the maximum power speed ?
in the manual they don't give you the number of turns to start with, because they don't want you adjusting the saw,I see most saws are 1 to 1 1/4 out to start

 

[MasterMech]

The only factory default settings I can find for the 445 are
Maximum power speed – 9600 RPM
Maximum recommended engine speed – 13,000 RPM
Idle speed – 2700 RPM
If I had a tach , would I be trying to set the high RPM 9600 and not exceed 13,000 ? If not, What do they mean by the maximum power speed ?
in the manual they don't give you the number of turns to start with, because they don't want you adjusting the saw,I see most saws are 1 to 1 1/4 out to start

9000 RPM will be where the saw makes the most power.

13000 RPM will be what you set the H setting to.

You can tune so long as you can get the saw started. A bit easier if it's somewhat close to start with however.

 

[pyroholic]

Are the numbers (rpm) and process for the L and LA settings going to be the same for all Stihl's with the only variants being the max rpm? If not where is this info at? specifically looking for specs for the 038 magnum, but need to know for my other saws too.

 

[MasterMech]

Are the numbers (rpm) and process for the L and LA settings going to be the same for all Stihl's with the only variants being the max rpm? If not where is this info at? specifically looking for specs for the 038 magnum, but need to know for my other saws too.

The specs are generally in your owners manual. Your 038 will tune exactly like the 460 in the vid but your factory max rpm is 12500 I believe. I would tune it by ear first and see where you end up. If you have it set at 13k or less and it's four-stroking out of the wood, I wouldn't worry about fattening it up to 12500.