MS 260 muffler mod help

[KMB]

I've been reading about muffler mods in this forum and I want to do one on my MS 260 (non-pro). I bought it with a 20" bar - it was my first saw, I bought it through a friend who knew someone who owns a Stihl dealership, so I didn't get good advice on a bar size. I should have asked/read here about recommendations on a bar size for my saw. Anyway, I'm looking into getting a 16" bar with a 8t sprocket. When my finances allow, I'll be looking to get a used 036 Pro/360 Pro (or 044/440) with a 20" bar for bigger stuff for selling firewood on the side. I'd love a new 361, but that's totally unrealistic right now - I got a wife, like to hunt, fish, handload/reload and other things that takes my money. So for now, I'm going to have to make do with my 260. I figure a muffler mod is an inexpensive way to get a little more performance from my saw. I just want to make sure I don't mess up what seems to be a easy procedure. I've searched the forum for 260 muffler mod threads, so I think I understand what to do, but I have a few questions (btw, any other inexpensive suggestions to mod my saw are welcome). I want a little more performance for when I want to use the 20" bar. I know it's crazy using that long of a bar with that small of a saw, but I have used it on some 18"+ diameter (approx.) wood and it was slowwww - but it got it done.
I plan on widening the existing hole in the 'muffler cover' (the spare parts list calls it an exhaust casing) and putting 2 more holes above and below the existing. I was going to put them to either side of the existing hole, but there is the screen mounting hole on one side. Do the new holes have to be in a horizontal line to match the exhaust port opening? Or is it okay to have them vertical like I plan to do. From more reading/searching, I've determined that my saw has a fixed jet carb - correct me if I'm wrong. Are there any adjustments to the carb that can or will be needed after the muffler mod? I wouldn't call myself a mechanic, but I am mechanically inclined a little - if that makes sense. If there's anything I have to be careful of when doing any mods to my saw - please let me know. I'm just careful by nature.

 

[Lawn Masters]

To answer your carb question, YES! you have to richen it up to allow more fuel to get to the motor so you're not running lean. how to adjust a fixed jet carb is one thing I admit, I dont know how to do, so I wont try to say anything about it.

 

[Big Woody]

I have an 026 pro with the fixed high speed carb as is your 260. I also was considering increasing the muffler opening as well. It is not a good idea to open up the muffler on your saw as you have no hi speed carb adjustment screw to compensate for the increased air flow. You must either switch out the jet in the carb or possibly drill it out. For a few years stihl had fixed high speed jets on these saws but you can find identical carbs with adjustable jets.

The best solution is to watch ebay and try to pick up a new or good used carb with an adjustable high speed jet to fit your saw (or get one from someone here). I found a new one on ebay for $14 shipped. I have it but haven't installed it yet. I think a new one retail might be $70 (thats a guess). Just search ebay on stihl 260 or 026. Most pictures don't show the jet screws so you have to email a question to the seller and ask if it is adjustable. I think you want the Walbro wt-426 carb (or the 427).

http://www.arboristsite.com/showthread.php?t=24654&highlight=Walbro+wt-426

 

[Fireaxman]

I know it's crazy using that long of a bar with that small of a saw, but I have used it on some 18"+ diameter (approx.) wood and it was slowwww - but it got it done.

I don't think it is crazy to expect your 260 to pull a 20" bar. When I bought my MS-260 I specificly asked my dealer if it would pull the 20" bar, and he assured me it would. Like you, I was very disappointed the first time I buried the bar in an oak. I took it back to the shop and got an 18" bar.

A year later I learned about the muffler modification. I think you are going to be pleasantly surprised at how much of a difference it makes on the 260. When I burn out this 18" bar I'm going back to the 20". Now that the saw is thoroughly broken in, and now that it can breathe, I am confident it will pull the 20" bar comfortably.

I have a lot of respect for my dealer. He has done some excellent work for me, especialy in re-vitalizing some older saws. That is why I was so surprised that the 20" bar did not perform well after his recomendation. I wonder now if he didn't just expect me to open up that muffler right from the start, but didn't want to tell me to do something unorthodox in his formal capacity as "Stihl Dealer".

My MS-460 has the same problem from the factory, can't breath through that one little exhaust hole. But when I bought the 460 I had already been warned by people on this web site and by my experience with the 260. Stihl actually sells a "Dual Port Exhaust Cover" for the 460, and I ordered one the day I picked up the 460. I wonder why they don't make one for the 260.

 

[davefr]

I have an 026 non pro and here's what I did:

1. Pull off the muffler and seperate the two halves. Thank Stihl for not having a one piece crimped muffler.
2. Inside you'll see a pencil eraser sized baffle hole. Widen it 3X. (ie drill two more holes alongside it and use a dremel tool to make it rectangular.
3. Now improve the muffler's final exit hole. Widen it with a dremel tool.
4. I've used the rule of thumb that the exit holes should be no less then about 75-80% the area of the exhaust port.
5. Now if you have a non adjustable carb remove it and pull off the top cover plate and diaphram.
6. There's a tiny screwed in brass insert. That's the High speed fixed jet. Remove it with a tiny screwdriver and get a set of numbered drills (ie 60 thru 80) and drill it out only to the next size up. (you can do it by hand since it's so tiny). If you look closely it's marked with a number. (ie my jet was .56mm and I went with the next size up numbered drill bit which resulted in the jet now being .571mm) There are much more elaborate modification methods but this will give you a much better running saw and won't cost you much.

 

[ShoerFast]

KMB
As I dont have a 260, I read just about everything there is if it has to do with drilling things to go faster!
But I did pick up on something you said,,,,

"I'm looking into getting a 16" bar with a 8t sprocket."

Please, as I said, I dont run a 260, but it sounds a little fast with a 8T drive?
IMHO, I would be looking at a 7T if it were my primary saw and your cutting full bar length.
Kevin

 

[Lawn Masters]

Ok, here's what I've done for muffler mods on the 024 style muffler, which is similar to the 026.

I went and cut the stock exhaust outlet much wider, then just refitted the spark arrestor screen, which still covers the whole thing, and looks TOTALLY stock, unless you took the cover off it.

 

[KMB]

KMB
Please, as I said, I dont run a 260, but it sounds a little fast with a 8T drive?
IMHO, I would be looking at a 7T if it were my primary saw and your cutting full bar length.
Kevin

I have read here about sprockets and that using a 8t sprocket for 'shorter' bars and that using a 7t sprocket for 'longer' bars work good. I was going to try the 16" bar/8t setup for comparison to the 16"/7t setup. I'll still be using the 7t for the 20" bar. I guess I'm looking ahead to when I can have 2 saws where my 260 will have a 16" bar on all the time and the bigger saw with a 20" bar. Thanks for your input. I'm not to proud to listen and learn.

 

[KMB]

Thanks all for the info thus far, it has helped - especially with my carb concerns. I don't feel comfortable modifying my High speed fixed jet, so I'm going to look into the WT-426 carb. When adjusting a carb, it sounds to me that having someone running my saw at full throttle in a cut (saw under load), and myself carefully adjusting the high speed adjustment is the way to do it. Or is there a better way? Any more info relating to 260 carb and muffler mods is welcome.

 

[davefr]

I was also somewhat hesitant modifying my fixed jet but it's really easier then it sounds. It's a 15 minute job.

The only concern is using the correct size screwdriver to remove the jet because it's soft brass and pretty tight in the carb's body. I think there's very little risk going .01 mm larger.

If you screw up the jet, it's only about a $5 part from Stihl.

Thanks all for the info thus far, it has helped - especially with my carb concerns. I don't feel comfortable modifying my High speed fixed jet, so I'm going to look into the WT-426 carb. When adjusting a carb, it sounds to me that having someone running my saw at full throttle in a cut (saw under load), and myself carefully adjusting the high speed adjustment is the way to do it. Or is there a better way? Any more info relating to 260 carb and muffler mods is welcome.

 

[KMB]

I was also somewhat hesitant modifying my fixed jet but it's really easier then it sounds. It's a 15 minute job.

The only concern is using the correct size screwdriver to remove the jet because it's soft brass and pretty tight in the carb's body. I think there's very little risk going .01 mm larger.

If you screw up the jet, it's only about a $5 part from Stihl.

I might give it a try. I have taken apart the carb on my grass trimmer and I put in a carb kit (diaphram and gaskets), cleaned it and put it back together and the trimmer is back running - so I should be able to handle opening the jet. I was looking in my spare parts list from Stihl and I think the jet is called an 'Inlet needle' - does that sond right? I'll be calling one of the local dealers to make sure they have one in case I screw up.

 

[davefr]

I might give it a try. I have taken apart the carb on my grass trimmer and I put in a carb kit (diaphram and gaskets), cleaned it and put it back together and the trimmer is back running - so I should be able to handle opening the jet. I was looking in my spare parts list from Stihl and I think the jet is called an 'Inlet needle' - does that sond right? I'll be calling one of the local dealers to make sure they have one in case I screw up.

No, the jet is called "Fixed Jet" for carb # WT-403.

Go here and download the 026 parts manual. Page 18 is the WT-403 carb. The fixed jet is illustration #11. Stihl part number for the .56mm jet is 1120 121 5600. I believe Stihl has other orifice sizes however I don't know the PN's. :

http://www.giftsofwood.com/stihl_info.htm

 

[KMB]

davfr,
Thanks alot for the link to the Stihl info manuals etc. I looked at my spare parts list (for MS 260) again and this time found the parts. For the WT-403A carb, my illustration #11 is a 'Fixed jet' (part #1120 121 5600) and illustration #31 is a 'Fixed jet 0.52' (part #1120 121 5602).
I'm assuming that if my saw is to lean (not enough fuel) that it will rev higher (like it does when it's about to run out of fuel) and that if it is to rich (to much fuel) that it will bog. And common sense tells me the more holes (or bigger holes) in the muffler - the bigger the opening in the jet has to be. Again, correct me if I'm wrong.

 

[jokers]

I have read here about sprockets and that using a 8t sprocket for 'shorter' bars and that using a 7t sprocket for 'longer' bars work good. I was going to try the 16" bar/8t setup for comparison to the 16"/7t setup. I'll still be using the 7t for the 20" bar. I guess I'm looking ahead to when I can have 2 saws where my 260 will have a 16" bar on all the time and the bigger saw with a 20" bar. Thanks for your input. I'm not to proud to listen and learn.

I`ve had quite afew 026/ms260s and they don`t pull an 8 tooth sprocket well at all when stock. Furthermore you have to remove the rim and install the rim/bar/chain as an assembly, at least when new. I don`t know if the chain will stretch enough to allow leaving the 8 tooth on during subsequent chain swaps because the saws are so weak like this that I never left an 8 tooth on.

Here`s a tip that will save you money over the long run and allow you more sprocket choices if you are so inclined. Buy an Oregon rim and drum kit for your 260 which will eliminate the need to run Stihl proprietary "Mini" spline rims. You can easily buy Oregon or GB rims for half the price of Stihl rims and they are just as good.

If you decide to keep your fixed jet carb after you open the muffler, check the metering lever height when you go inside to bore the jet. It`s been so long since I`ve done one that I`m not absolutely sure but I believe that the lever should be flush with the surrounding casting. Stihltech will be able to tell you.

Russ

 

[jokers]

davfr,
Thanks alot for the link to the Stihl info manuals etc. I looked at my spare parts list (for MS 260) again and this time found the parts. For the WT-403A carb, my illustration #11 is a 'Fixed jet' (part #1120 121 5600) and illustration #31 is a 'Fixed jet 0.52' (part #1120 121 5602).
I'm assuming that if my saw is to lean (not enough fuel) that it will rev higher (like it does when it's about to run out of fuel) and that if it is to rich (to much fuel) that it will bog. And common sense tells me the more holes (or bigger holes) in the muffler - the bigger the opening in the jet has to be. Again, correct me if I'm wrong.

It`s highly unlikely that you will need a .52 jet, a bored out .56 seems more like the norm. Since these jets are about $5 each, you are better off finding an adjustable carb on eBay if you don`t want to ream yours.

 

[davefr]

davfr,
Thanks alot for the link to the Stihl info manuals etc. I looked at my spare parts list (for MS 260) again and this time found the parts. For the WT-403A carb, my illustration #11 is a 'Fixed jet' (part #1120 121 5600) and illustration #31 is a 'Fixed jet 0.52' (part #1120 121 5602).
I'm assuming that if my saw is to lean (not enough fuel) that it will rev higher (like it does when it's about to run out of fuel) and that if it is to rich (to much fuel) that it will bog. And common sense tells me the more holes (or bigger holes) in the muffler - the bigger the opening in the jet has to be. Again, correct me if I'm wrong.

I'm by no means an expert, but by opening up the muffler the saw will tend to run faster and hence need to be richened up a tad to keep it from over reving.

It'll take good eyes or a magnifying glass but the jets in our saws are stamped with the size right on the top. I believe non pros all use .56mm. Pros and high elevation saws used the .52mm jet.

Based on the pasts posts I've read, Stihltech suggests that a .01mm increase is about all that 026's normally require. The opened up muffler combined with a .01mm increase sure makes my 026 run well and I'm still slightly in the "blubber zone" at full speed. (I'd estimate 20% increase from stock)

 

[jokers]

Overreving is merely a symptom of running lean and you won`t have to worry about overreving in a cut.

My 260 Pros all had .56 jets. What jet you get may be related to where the saw was shipped to.

Russ

 

[KMB]

I`ve had quite afew 026/ms260s and they don`t pull an 8 tooth sprocket well at all when stock. Furthermore you have to remove the rim and install the rim/bar/chain as an assembly, at least when new. I don`t know if the chain will stretch enough to allow leaving the 8 tooth on during subsequent chain swaps because the saws are so weak like this that I never left an 8 tooth on.

Here`s a tip that will save you money over the long run and allow you more sprocket choices if you are so inclined. Buy an Oregon rim and drum kit for your 260 which will eliminate the need to run Stihl proprietary "Mini" spline rims. You can easily buy Oregon or GB rims for half the price of Stihl rims and they are just as good.

If you decide to keep your fixed jet carb after you open the muffler, check the metering lever height when you go inside to bore the jet. It`s been so long since I`ve done one that I`m not absolutely sure but I believe that the lever should be flush with the surrounding casting. Stihltech will be able to tell you.

Russ

Thanks for the info regarding 8t vs 7t sprockets. Regarding checking the metering lever, is that the same as the 'Inlet control lever' (Stihl illustrated parts book)? If so, is the adjustment made by the spring?

 

[KMB]

It`s highly unlikely that you will need a .52 jet, a bored out .56 seems more like the norm. Since these jets are about $5 each, you are better off finding an adjustable carb on eBay if you don`t want to ream yours.

I do like the fact that the adjustable carb can do just that - be adjusted. It can be adjusted when the saw is all together and running versus taking the carb apart to deal with the fixed jet. But from what I've read here that opening the fixed jet by approx. 0.01mm . will take care of things, so I would have to go into the carb only once, but stuff happens sometimes.

 

[buck futter]

Why not open up the muffler and see how the saw runs with the muffler mod? Even after a muffler mod on my 025 the saw was still running rich. How does your saw run now, what does the plug look like? If you are making mods what would it hurt to do one at a time? If its lean, you'll know it, if it still 4 strokes than leave it alone. I ended up buying a carb off ebay but that was more because I'm a hopeless tinker.

As far as the two man tuning method while the saw is in the wood, I think it opens up a whole bunch of variables, type of wood, chain condition, raker height, down pressure by the operator. However to each there own.

Regards
Lucky