need help tuning a used MS260

[Deleted member 27831]

I am refurbishing a MS260 I bought used and am running into an unexpected problem.

So far I have replaced the air filter, the fuel filter and fuel line, the spark plug, and I removed the spark arrestor. I adjusted the carb. screws per the manual's recommendation. New bar and chain too.

The saw starts well, idles well, and cuts fine at lower speeds. But at full throttle, for lack of a better term, it doesn't have any guts. It bogs down immediately when I try to cut at full throttle. I gave up trying to cut through a 6" mulberry. Also, it seems to be running a little fast at full throttle, but maybe I'm just not used to this saw.

Any suggestions as to what I should try before I give up and bring it to the shop for a look-over? I'm a mechanically minded person, but have almost no small engine experience so its going to have to be easy stuff if I'm going to be able to do it.

Thanks,

 

[AKDoug]

Does this 260 have both a H and L screw? If so, turn the H screw out about 1/4 turn and try again. Sounding a little fast while not in the wood, and bogging in the wood is often a lean condition.

 

[50blues]

When you had the muffler off did you look in at the side of the piston? If so was it smooth and nice looking or scratched up? Low compression could cause what your describing, but so could a dirty carb. time to dig in.

 

[Deleted member 27831]

Thanks for the input y'all. As it turns out it was just the high end throttle was a little rich. Its a bit confusing on this particular saw since you're supposed to turn the H screw 3/4ths of a turn from stop, but it only just goes 3/4ths of a turn. I turned it back 1/4th of a turn and its running fine now. I may try to fine tune a bit more later.

 

[windthrown]

It sounds to me like you re-tuned it too lean, unless someone re-jetted the carb at some point. I would pull the carb limiters and trim the tabs, and re-seat them. Usually at full stop they are still too lean and need about another 1/8 turn to run right. Warm the saw up and run it in wood at WOT full throttle for a full minute, then kill it. Let it cool down and pull the plug. It should be an even tan color. If it is white, it is too lean. Also if it is running too clean at WOT out of the wood, it is too lean. It should burple (4-stroke) at WOT out of the wood, and clean up in the wood. I run all Walbro 194 carbs in my 026/260 saws, they are the fattest carbs if the series, and even they tend to run lean at the 3/4 turn default setting.

 

[Philip Wheelock]

From the Stihl MS260 Service Manual:

Adjust idle speed with a tachometer. Adjust specified engine speeds within tolerance of ± 200 rpm.

1. Adjust engine speed with idle speed screw (LA) to 3,600 rpm.

2. Turn the low speed screw (L) clockwise or counterclockwise to obtain the maximum engine speed.
If this speed is higher than 3,700 rpm, abort the procedure and start again with step 1.

3. Use the idle speed screw (LA) to set engine speed again to 3,300 rpm.

4. Set the engine speed to 2,800 rpm with the low speed screw (L).

5. Set maximum engine speed with the high speed screw (H) (see Specifications) (14,000 rpm for ms260)

 

[blsnelling]

IMHO, tuning by plug color on a saw is was too subjective and prone to error. I'd recommend that you take it to the dealer and have them tune it with a tach to 14,000 RPMs.

 

[z71mike]

I'd trim the tabs, watch a youtube video on tuning, and have at it.

 

[pioneerguy600]

It sounds to me like you re-tuned it too lean, unless someone re-jetted the carb at some point. I would pull the carb limiters and trim the tabs, and re-seat them. Usually at full stop they are still too lean and need about another 1/8 turn to run right. Warm the saw up and run it in wood at WOT full throttle for a full minute, then kill it. Let it cool down and pull the plug. It should be an even tan color. If it is white, it is too lean. Also if it is running too clean at WOT out of the wood, it is too lean. It should burple (4-stroke) at WOT out of the wood, and clean up in the wood. I run all Walbro 194 carbs in my 026/260 saws, they are the fattest carbs if the series, and even they tend to run lean at the 3/4 turn default setting.

I agree with you 100% , this is how I tune chainsaws but for the average saw owner they haven`t a clue to what we are talking about when we describe this operation. Therefor the tach is the next best option for them.

 

[windthrown]

I usually use a tach, but I also tune a saw by ear, then by cuts, then I verify with a plug test. I have never lost a saw engine to scoring, and I have owned over 100 saws and lots of other 2-stroke devices. Ears work a lot better for me for fattening a saw up at WOT, where a tach may be too lean or too fat. Not everyone has a $100 digital high RPM tach, and they are really not required. I tuned my saws w/o a tach for many years myself. Madsens has an excellent tune by ear method online, and it is pretty good and simple. IMO, if the OP is tearing saws down and rebuilding them, he should be able to tune a saw w/o dragging it into a dealer or shop, tach or no tach. I have found that the default setting on Stihls will really not be that far off either, as long as they are stock. Once you open up the muffler or rejet the carbs, or do any kind of porting, that goes out the window though.

My complete tuning method: I make sure that the muffler screen is open and the AF is clean. I put the B&C I wanna run on the saw and tune it at the altitude I am cutting at. I can go up and down about 6k feet in 45 minutes here. Then I seat and reset the jets to the default values, then tune the low end and idle with a tach, then I tune the high end with a tach. But then I use my ears to more finely adjust the WOT for burple, and then make some cuts to test the WOT in and out of the wood. Burple out of the wood WOT, cleans up in it. No fade or fall off, re-adjust if not right. Re-check with the tach. Then if it is a rebuilt engine or carb or a new saw to me, I run them WOT in the wood and verify with the plug color test.

Also note that Stihl publishes max RPM values for their saws that are 500 RPM lower than the actual redline. The real max RPM on a 260 is 14.5k. So you can go higher w/o blowing them up.

 

[Mikesawed]

From the Stihl MS260 Service Manual:

Adjust idle speed with a tachometer. Adjust specified engine speeds within tolerance of ± 200 rpm.

1. Adjust engine speed with idle speed screw (LA) to 3,600 rpm.

2. Turn the low speed screw (L) clockwise or counterclockwise to obtain the maximum engine speed.
If this speed is higher than 3,700 rpm, abort the procedure and start again with step 1.

3. Use the idle speed screw (LA) to set engine speed again to 3,300 rpm.

4. Set the engine speed to 2,800 rpm with the low speed screw (L).

5. Set maximum engine speed with the high speed screw (H) (see Specifications) (14,000 rpm for ms260)

How do I go about this when I only have 1 screw for the H L as well as the LA screw? I finally picked up a tach (Smart Tach TA500) I found on marketplace for $50. It retails for $250-$400 according to Google. It not only reads the RPM wirelessly but also gives the spark plug burn time as well as the voltage. It also has a setting to record the minimum and maximum of any of the 3 readings it is capable of picking up. So it can be set to display the current RPM as if fluctuates as well as display both the minimum and maximum RPM for the duration of the reading. And when do the same the spark plug voltage and burn time. Some of that in sure is better used on a car or truck ignition system, but hey the rest of the tachs I saw only did RPM and like operation hours so this one seemed like it would be more useful.

 

[irhunter]

How do I go about this when I only have 1 screw for the H L as well as the LA screw?

Are you talking about a MS260?

 

[bwalker]

How do I go about this when I only have 1 screw for the H L as well as the LA screw? I finally picked up a tach (Smart Tach TA500) I found on marketplace for $50. It retails for $250-$400 according to Google. It not only reads the RPM wirelessly but also gives the spark plug burn time as well as the voltage. It also has a setting to record the minimum and maximum of any of the 3 readings it is capable of picking up. So it can be set to display the current RPM as if fluctuates as well as display both the minimum and maximum RPM for the duration of the reading. And when do the same the spark plug voltage and burn time. Some of that in sure is better used on a car or truck ignition system, but hey the rest of the tachs I saw only did RPM and like operation hours so this one seemed like it would be more useful.

Fixed jet carb. Your effed for tuning the high side. Chuck the carb in the trash and put a WT-194 on it.

 

[bwalker]

https://www.ebay.com/itm/3535812881.../eJ2e+IWXc08NkptL8AyOkpqmG|tkp:Bk9SR9Kt1sqnYQ

 

[Mikesawed]

What is the procedure if it only has the L and idle screws. The process you posted on works on saws that have the H & L with the idle screw. Mine only has the L with the idle screw so the process you posted from the manual won't work.

From the Stihl MS260 Service Manual:

Adjust idle speed with a tachometer. Adjust specified engine speeds within tolerance of ± 200 rpm.

1. Adjust engine speed with idle speed screw (LA) to 3,600 rpm.

2. Turn the low speed screw (L) clockwise or counterclockwise to obtain the maximum engine speed.
If this speed is higher than 3,700 rpm, abort the procedure and start again with step 1.

3. Use the idle speed screw (LA) to set engine speed again to 3,300 rpm.

4. Set the engine speed to 2,800 rpm with the low speed screw (L).

5. Set maximum engine speed with the high speed screw (H) (see Specifications) (14,000 rpm for ms260)