Stihl MS291 questions

[ColdStihl]

I hope you don't mind me borrowing your pic to illustrate some clarification.

With the red arrow, this is what I grind off for 360 adjustment, correct? I think so. If I remove the limiter, turn the white adjuster 1/2 turn out (orange arrows), and then replace the limiter, in theory I just gained 1/2 turn of rich adjustment, correct?

As it stands, my stock saw can turn in or go leaner 3/4 turn. As I said before, the saw came to me as rich as it will go. No chance for muffler mod and, in reality, not as rich as I would prefer even when keeping the muffler stock.

 

[ColdStihl]

Oh, by the way, is there a limiter on the L adjustment? I seem to have plenty of adjustment on that one. Just wondering.

Edited: For clarity.

 

[SAWMIKAZE]

I really wish those photos were clearer so that I can see the tips better. I can't tell if the top driver is threaded or smooth, and I can't tell if the bottom driver is flat head. If you can retake your pic on Macro (flower icon) setting and get closer to the tips, I can see what I'm working with. If you can't, no big deal. Totally appreciate your contribution!

 

[ColdStihl]

View attachment 363213

Rock on! Thank you. Is the one on the left square at the very tip? You wouldn't happen to know the thread pitch for the one on the right?

 

[7sleeper]

Hi guys im new to this site hope to get to know yall, this is my 1st message
Anyway was wondering if unlimited adjustment(richening) will be enough for muffler mod

I believe you will have to learn first something about carb setting before you "screw up" your carb settings by "screwing around" without knowing what you are doing!

7

 

[Weesa20]

I hope you don't mind me borrowing your pic to illustrate some clarification.

With the red arrow, this is what I grind off for 360 adjustment, correct? I think so. If I remove the limiter, turn the white adjuster 1/2 turn out (orange arrows), and then replace the limiter, in theory I just gained 1/2 turn of rich adjustment, correct?

As it stands, my stock saw can turn in or go leaner 3/4 turn. As I said before, the saw came to me as rich as it will go. No chance for muffler mod and, in reality, not as rich as I would prefer even when keeping the muffler stock.

View attachment 363212

There are 2 limiters...in the pic with the added arrows, if you look on the right hand side at about 3 o'clock, you can see the inner white edge is square and there is a small melted blob...that is what is left of the plastic limiter. Some guys will take these out and replace them with a new one that has had the limiter cut off (I think you need the special tools for this...I seriously doubt a Stihl Authorized dealer will sell these tools). In stock form, before being melted, the plastic limiter sticks out and interfaces with the metal ridge (red arrow), thus limiting the adjustment to ~3/4 of a turn. With it removed, you have full adjustment as the left over white plastic and screw will turn as much as you want. Pic with the original plastic limiter "painted" back in with blue arrow showing how it limited adjustment by hitting the rib/ridge (red arrow).


This leaves the metal limiter- you could grind off the metal rib/ridge on the inner wall and have full adjustment or you could tune the saw without the metal limiter and then put it back in, which should leave you with the original 3/4 turn of adjustment but the screw will be set to a richer setting so it won't really matter. Ideally you would have 3/8 of turn in either direction (lean or rich)- or you could just take out the metal limiter when you want to readjust the saw and then put it back.

I believe the low side is fully adjustable- EPA doesn't care about the low side for the most part.

 

[ColdStihl]

Great info, and exactly what I wanted to know. Highlighting the missing tab of white plastic explained everything. It seems that my inquiry about gaining another half turn out could not be done without some sort of mod to the adjuster or carb housing. So, I take it with the white tab trimmed off, you still need to pull the metal limiter cap every time in order to fully adjust the saw?

They really went the extra mile to prevent tampering on this thing, but I am really enjoying the learning and discussion.

 

[Rockjock]

Guy you are over thinking this. The tools that were listed are at the dealer for you to buy. You remove the limiter IF you damage it just buy another one and keep it as a spare. Next you use the tool to adjust the carb as you desire then put back the old limiter cap or leave it out . Down the road if you have an issue and want to take it in for service you can put in the new limiter cap and be done with it.

 

[Weesa20]

Yes, you would need to pull the metal cap/limiter to make it fully adjustable. But, once tuned properly, unless you modded it more, 3/4 of a turn should be sufficient for changes in ambient environment or altitude, I would think. Pulling the metal cap/limiter is very easy.

This pic shows how the metel ridges (purple arrows) on the cap interface with the ridge on the cavity (original red arrow)...you could grind this off along with modifying the plastic limiter, and have the same effect as grinding the ridge off the inside of the cavity to make it fully adjustable, but this cap might be weakened too much. You can also see where the notch (brown arrow) interfaced with the white plastic limiter tab (in stock form).

 

[Weesa20]

I don't think I'm over thinking this. Just my opinion. I don't like to spend money, even if I could buy the tools and the replacement limiter. My dealer won't sell me the tool to adjust the carb on FS trimmers or BR blowers, so why would he sell me these?

I know where to get the FS/BR carb tool but it would also cost me $30. Maybe your dealer is different. I'm just offering another simpler, cheaper, faster way to get to the same end.

 

[ColdStihl]

Guy you are over thinking this. The tools that were listed are at the dealer for you to buy. You remove the limiter IF you damage it just buy another one and keep it as a spare. Next you use the tool to adjust the carb as you desire then put back the old limiter cap or leave it out . Down the road if you have an issue and want to take it in for service you can put in the new limiter cap and be done with it.

I'm an engineer so, guilty as charged. I would like to know everything about it so I can make an informed decision on what direction I want to go.

Please clarify something for me. After removing the metal limiter cap, doesn't the tab on the white adjuster part prevent you from FULL tuning capability? It seems to me that you are limited by the tab and without modification (trimming) you can only go so rich even with the limiter cap removed. In stock configuration, I am wondering if it's the plastic tab or the metal limiter cap that is the first hard stop that I'm feeling, or both. Would go a long way in knowing what I can do to limit modification for the warranty's sake. As alluded to in my first post, I am not a fan of making irreversible modifications and potentially nullifying my warranty. Yes, I know the risks of any modification. I'd like to mitigate detection as much as possible. Call me sneaky.

I'll inquire with my dealer about those tools. He's on vacation this week.

 

[ColdStihl]

Yes, you would need to pull the metal cap/limiter to make it fully adjustable. But, once tuned properly, unless you modded it more, 3/4 of a turn should be sufficient for changes in ambient environment or altitude, I would think. Pulling the metal cap/limiter is very easy.

This pic shows how the metel ridges (purple arrows) on the cap interface with the ridge on the cavity (original red arrow)...you could grind this off along with modifying the plastic limiter, and have the same effect as grinding the ridge off the inside of the cavity to make it fully adjustable, but this cap might be weakened too much. You can also see where the notch (brown arrow) interfaced with the white plastic limiter tab (in stock form).

Maybe you already answered my previous questions, but I'll ask this. In stock form, does the metal limiter drive the white plastic adjuster when using the standard screwdriver? If it does, then there has to be a keyway that needs to line up in order to re-install the metal cap. Correct me if I am wrong. In other words, if I removed the metal cap, then adjusted the white plastic part to a proper tune, wouldn't the limiter cap hit an obstruction (the metal tab) within the carb opening upon re-install?

 

[Rockjock]

I'm an engineer so, guilty as charged. I would like to know everything about it so I can make an informed decision on what direction I want to go.

Please clarify something for me. After removing the metal limiter cap, doesn't the tab on the white adjuster part prevent you from FULL tuning capability? It seems to me that you are limited by the tab and without modification (trimming) you can only go so rich even with the limiter cap removed. In stock configuration, I am wondering if it's the plastic tab or the metal limiter cap that is the first hard stop that I'm feeling, or both. Would go a long way in knowing what I can do to limit modification for the warranty's sake. As alluded to in my first post, I am not a fan of making irreversible modifications and potentially nullifying my warranty. Yes, I know the risks of any modification. I'd like to mitigate detection as much as possible. Call me sneaky.

I'll inquire with my dealer about those tools. He's on vacation this week.

LOL I too am a P.Eng. so I know the affliction all too well. Once the cap is removed you have full range of movement. 1 tool is used to remove the cap, it is threaded in and the limiter cap is pulled out. The second tool is used to adjust the carb.

 

[Weesa20]

Since the metal "saddles" the plastic, I think the metal is your first hard stop. As rockjock stated, if you can find the tools and buy a replacement plastic limiter, then you can always put it back to stock...no matter which method you use.

The muffler would be a different story though. You will need a replacement and, if your dealer really wants to catch you, he will probably be able to tell that the muffler has been removed previously (not sure if this voids the warranty as I have only bought one new Stihl and didn't pay any attention to the warranty). The bolts will have tool marks, there won't be as much carbon/rust/wear and tear on the muffler as there should be (unless you find a used one) and the gasket will release much easier than on a saw that has never had the muffler removed.

Not sure you could avoid detection of previous mods. Would depend on how tough your dealer is.

 

[ColdStihl]

LOL I too am a P.Eng. so I know the affliction all too well. Once the cap is removed you have full range of movement. 1 tool is used to remove the cap, it is threaded in and the limiter cap is pulled out. The second tool is used to adjust the carb.

Perfectly explained. Thank you!

 

[Weesa20]

LOL I too am a P.Eng. so I know the affliction all too well. Once the cap is removed you have full range of movement. 1 tool is used to remove the cap, it is threaded in and the limiter cap is pulled out. The second tool is used to adjust the carb.

Not sure that this is correct...you need to remove the metal "cap" AND trim or remove the white plastic limiter in order to have full range of motion. With only the metal removed, you can only turn it as much as you can with the metal cap installed.

The metal interfaces with the white plastic in two areas to "drive" it...one is the slot (brown arrow) that saddles the limiter tab. The other is a rectangle area that slides over a corresponding elevated rectangle portion of the white plastic. You can kind of see how the metal changes from round to rectangle in the pic with the purple and brown arrows. It is just a simple press fit to keep it in place.

 

[ColdStihl]

Since the metal "saddles" the plastic, I think the metal is your first hard stop. As rockjock stated, if you can find the tools and buy a replacement plastic limiter, then you can always put it back to stock...no matter which method you use.

The muffler would be a different story though. You will need a replacement and, if your dealer really wants to catch you, he will probably be able to tell that the muffler has been removed previously (not sure if this voids the warranty as I have only bought one new Stihl and didn't pay any attention to the warranty). The bolts will have tool marks, there won't be as much carbon/rust/wear and tear on the muffler as there should be (unless you find a used one) and the gasket will release much easier than on a saw that has never had the muffler removed.

Not sure you could avoid detection of previous mods. Would depend on how tough your dealer is.

I would think that with the proper tools, I can do what I need to do without apparent detection. I realize that using homemade tools may knacker the look of the parts, which I will try to avoid. At some point I will have to $hit or get off the pot!

I won't dive into muffler mod just yet. I'll leave that on the back burner. I'm more interested in getting my saw properly tuned. I can tell it runs on the lean side on the top end. I did muffler mod my old saw and wondered why I hadn't done that 4 years ago. The good thing about that saw was it had no limiters, only a "single D" driver was needed.

 

[ColdStihl]

Not sure that this is correct...you need to remove the metal "cap" AND trim or remove the white plastic limiter in order to have full range of motion. With only the metal removed, you can only turn it as much as you can with the metal cap installed.

The metal interfaces with the white plastic in two areas to "drive" it...one is the slot (brown arrow) that saddles the limiter tab. The other is a rectangle area that slides over a corresponding elevated rectangle portion of the white plastic. You can kind of see how the metal changes from round to rectangle in the pic with the purple and brown arrows. It is just a simple press fit to keep it in place.

That's what I was worried about. So then, could the white adjuster be pulled out and re-timed to the other side of the metal tab thereby giving you a lot more range, or will the metal cap re-install prevent that ?

 

[Rockjock]

Perfectly explained. Thank you!

Hardy perfectly explained but we as Engineers are always blamed for making something that can not be serviced! We have the added ability to look at things from both sides, the design and the end user. The cap is to stop the novice person from adjusting the carb, remove the cap then it is adjustable. So if I were you I would get the tools, they are like 5 bucks total I should think.

 

[Rockjock]

Not sure that this is correct...you need to remove the metal "cap" AND trim or remove the white plastic limiter in order to have full range of motion. With only the metal removed, you can only turn it as much as you can with the metal cap installed.

The metal interfaces with the white plastic in two areas to "drive" it...one is the slot (brown arrow) that saddles the limiter tab. The other is a rectangle area that slides over a corresponding elevated rectangle portion of the white plastic. You can kind of see how the metal changes from round to rectangle in the pic with the purple and brown arrows. It is just a simple press fit to keep it in place.

I think the point is to remove the limiter cap and make the adjustment and then IF you want to the metal cap back on. IF you were t cut away the plastic then it could be spotted right away. The saw is sold in 160 different countries so I would think adjustments would vary quite a bit. I wish I had a 271 or 291 so I could say for certain.