MS 291 performance advice

[dsleighton]

Hello everyone,

I've been reading AS periodically for about a year but this is my first time posting. I have spent a lot of time reading previous posts trying to answer my questions, but at some point, you've got to go right to the source! I have at least some experience with small machines and chainsaws, perhaps having cut 10 cords of wood in my life. I have owned an MS 291 for about 2.5 years and have used it to cut about 5 cords of wood. I would guess in total I have used about 8-10 tanks of fuel, but certainly less than 15. The saw has been slow to rev up, and I don't think I am achieving good high rpms/performance, and not sure if that's break in, tuning, muffler, or all of the above. In short, I would like some advice on carb tuning and possibly muffler modding.

As for the carb, I only recently decided to check, and found the H adjustment to be set fully counterclockwise. After watching videos here, I went to WOT, and turned the H screw the 3/4 turn clockwise allowed by the limiter, and noticed absolutely no change in saw noise (I did notice changes for L and LA). Does this seem realistic given I still have a stock saw (limiter present) or should there be a change? I have looked at pictures and think I could handle getting around the limiter problem if needed.

As for the muffler, I did a very small MM to an old 025 I used to have, but the muffler on the 291 is all crimped up, and I can't seem to figure out how to remove it/open it to at least clean (or remove) the spark arrestor or possibly increase the exhaust hole diameter. Facing the saw from the tip of the bar, there is a hole on the left of the muffler where I think I can see screen inside... is this the intake hole? What are the two things on the front of the muffler?

I only cut firewood for supplemental heating for my family, so I'm not looking to spend hours modifying the saw to the limit; I just want to feel like I'm reaching the saw's reasonable potential. Thanks to all in advance.

 

[Rockjock]

This is a good place to start to mod the 291
http://www.arboristsite.com/community/threads/muffler-mod-ms291-style.248665/

 

[dsleighton]

Thanks RockJock. That is one of the threads I have looked at a number of times and will plan to use should I decide to made modifications. One thing I'm really hoping to get feedback on is if its normal for me to get no throttle response by adjusting high H screw within the limiter limits, and if essentially I am "required" to remove the limiter to properly tune my saw. Or, should/could I bring it back to my dealer and allow him to remove the cap, tune it, and replace the cap? As far as the muffler, I'd really like to know how to open it and check/remove the screen, which I haven't seen in any of my searches. I read some references to heating it up and undoing the crimping, which I would prefer to avoid.

Dave

 

[Rockjock]

Thanks RockJock. That is one of the threads I have looked at a number of times and will plan to use should I decide to made modifications. One thing I'm really hoping to get feedback on is if its normal for me to get no throttle response by adjusting high H screw within the limiter limits, and if essentially I am "required" to remove the limiter to properly tune my saw. Or, should/could I bring it back to my dealer and allow him to remove the cap, tune it, and replace the cap? As far as the muffler, I'd really like to know how to open it and check/remove the screen, which I haven't seen in any of my searches. I read some references to heating it up and undoing the crimping, which I would prefer to avoid.

Dave

Dave the shark fin mod I think works very well on the 291, the placement of the fins bypasses the screen if I am not mistaken. also the limiters by definition limit the adjustment to the H screw. I did try on a MS 441 that was stock to make the adjustment with the limiter in place and I heard no difference at all in RPMS so I think, in this case, you are right it is normal. I can tell you the threads here are very detailed and there are many that have done these mods with great success. The process is similar for the MS 361 and people have stated it is a different saw all together. I have no reason to think the 291 would be no different.

 

[dsleighton]

Last night I was able to get the limiter out with a drywall screw. Maybe this is not the case for everyone, but it seemed to need to be rotated fully rich (CCW) to pull out, which was slight hassle since obviously the drywall screw rotates everything clockwise as you tighten it up. I have a 2mm hex key and played around with the H adjustment but it was after 8pm and so I didn't want to fire up the saw and actually do any tuning.

If I understand correctly, I could adjust the H screw to where I want it (slight burble), replace the limiter, and then have the 3/4 turn adjustment range in a range that is actually useful? For my purposes that would be preferable to grinding and cutting out pieces to make the carb fully adjustable. I am thinking about adding some muffler "shark fins" first.

 

[Rockjock]

Last night I was able to get the limiter out with a drywall screw. Maybe this is not the case for everyone, but it seemed to need to be rotated fully rich (CCW) to pull out, which was slight hassle since obviously the drywall screw rotates everything clockwise as you tighten it up. I have a 2mm hex key and played around with the H adjustment but it was after 8pm and so I didn't want to fire up the saw and actually do any tuning.

If I understand correctly, I could adjust the H screw to where I want it (slight burble), replace the limiter, and then have the 3/4 turn adjustment range in a range that is actually useful? For my purposes that would be preferable to grinding and cutting out pieces to make the carb fully adjustable. I am thinking about adding some muffler "shark fins" first.

What you could do is drill out the centre of the limiter cap and that way you will have easy access to the 4mm adjustment screw. I have a newish MS 261 that IIRC has the same sort of limiter and that will be my plan once I see it it's rebuild. Oh and the shark fin muffler modification.

 

[67L36Driver]

Pull the limiters and Throw them away! Open up the muffler! At least make the outlet less restrictive.

Set H & L 1 1/2 turns open from lightly seated and go from there.

 

[7sleeper]

I am against throwing away the limiters! Actually they are highly valuable original Stihl limiters!!! The correct way to use this highly valuable asset is to proceed in the correct manner and planning.

First off:
Collect ALL parts and chips you are remouving off your saw!!!

Second:
Assort these pieces in a pleasing manner!!!

Thrid:
Cast your pieces in a clear synthetic resin!!!

Fourth:
Place cast block on your workbench to always remind you of your first steps to the dark side...














Naw forget that!

To be honest, personally I would first off go to your stihl dealer and have him set the carb correctly! He should use a tach to be sure about the critical settings. Only after his attemps to make it run better would I consider a muffler mod.

7

 

[67L36Driver]

His futil attempts.

There fixed it for you.

 

[dsleighton]

His futile attempts are likely to be slightly less futile than my newbie attempts! I've watched the videos and listened to recordings, so I think I can get things to the right area, and then err a little on the side of rich. As for the limiter, does it prevent the adjustment screw from walking, or could I feasibly just leave it out permanently and just use the hex wrench to adjust if and when I want?

I think the best idea for now given my saw is probably just beginning to break in is to give a good adjustment, then after a few more tanks decide if I want to dive into the muffler business. In a few more tanks I'll be effectively done till fall, like I said I'm really only doing a few cords per year

 

[dsleighton]

UPDATE: I decided to keep the limiter in because I'd rather one tool to adjust the carb rather than two using a screwdriver and one a hex wrench. So I ended up using a dremel to grind down the burr that's keyed for the limiter; it took me all of 4 minutes to do it cautiously, then I used compressed air to clean out the metallic dust. I have full adjustment now, and am looking forward to playing around with it this week. I also sent a PM to Vince regarding his mod of the 291, he gave me some very helpful replies and I think I will also end up "opening up" the muffler. Who doesn't love using the dremel?

Thanks to all who replied to give me the confidence to do these modifications. I've learned a tremendous amount from this site and am highly grateful!