Adjusting H screw only for milling/ General tuning questions

[marti384]

Just found out my MS391 H screw is basically non adjustable for richer settings, while waiting for a response to this thread I turned the screw in to seat and back out to original (factory )setting...3/4 in 3/4 out nothing more then this! 3/4 out is where it was and the max!

Your 3120 most likely isn't adjustable on the high side either. I have yet to see a picture of a factory 3120 carb with a h screw.

 

[Andyshine77]

16:1 Mobil 30W non-detergent like in the 1960s?

I prefer used 10w30 myself.[emoji41]

 

[John J.]

Your 3120 most likely isn't adjustable on the high side either. I have yet to see a picture of a factory 3120 carb with a h screw.

Yeah my 3120xp is limited by a 9600rpm? coil and no H speed adjustment, just realized I've become a collector of EPA saws WTF! Haha I think you can purchase an adjustable carb for the 3120 or enlarge the orifice on the fixed H jet.
I guess my only option to richen up the MS391 H screw is to move to the mile high city and leave the H screw 3/4 open (max) living dangerous lol.

 

[MattG]

I guess my only option to richen up the MS391 H screw is to move to the mile high city and leave the H screw 3/4 open (max) living dangerous lol.

Or buy a nice old saw....and refurbish it till it's an awesome piece of old school engineering

 

[John J.]

Or buy a nice old saw....and refurbish it till it's an awesome piece of old school engineering

I have a few old saw but I wanted newer saws ready to run with safety features, might have went too new nothing but safety and limitations haha

 

[MattG]

I have a few old saw but I wanted newer saws ready to run with safety features, might have went too new nothing but safety and limitations haha

Yo, I'm a homeowner with the odd tree to prune and like cutting our own wood for our log-burner. First I had a new MS211....but found it a bit boring... now I've got an MS341, 064, and 2 x MS200T. Now I'm completely addicted....love repairing and running the old ones...and just like cars, the old ones are the best in my book!

 

[SeMoTony]

Just found out my MS391 H screw is basically non adjustable for richer settings, while waiting for a response to this thread I turned the screw in to seat and back out to original (factory )setting...3/4 in 3/4 out nothing more then this! 3/4 out is where it was and the max!

yur saw prolly has adjustment limiting tabs on plastic piece on screws. Taking out the plastic piece to cut off the limit tab is against the law for saw shops. Its like the tab of info on your mattress .....you can take it (the limit tab ) off with a snip or file to allow further adjustment than big brother feels we should have (-;

 

[Justsaws]

Strongly recommend tuning the saw rich both in the high and low circuit if possible. Getting the saw good and hot while cutting and then letting it idle tuned typically or factory might not be a good idea.

Generally I will set the idle rich enough that it barely stays running after it cools down, very lopey sounding. High side goes as rich as possible while still maintaining the appropriate RPMs loaded during the cut. The Stihl 391s would benefit from a bit more fuel on the idle if your are going to mill with it, also if you are going to mill a lot with that saw(1/2 gallon of fuel plus per milling) try letting it idle while sitting normal, not on the side as though you were still milling with it. Prop it against something and do not just shut it off after making a long cut. It is very easy to heat soak the crap out of a milling saw, may not cause bad immediate damage however could drastically shorten the life of the expensive parts, mostly bearings and everything that gets damaged when bearings go bad in a saw at WOT on its side. Make sure you are pushing on the mill and not the saw.

If your eyes and nose are burning from fumes and your saw is oozing un burnt fuel, might want to back off a bit.

32:1 , 32:1, 32:1, 32:1, 32:1, 32:1....

 

[John J.]

yur saw prolly has adjustment limiting tabs on plastic piece on screws. Taking out the plastic piece to cut off the limit tab is against the law for saw shops. Its like the tab of info on your mattress .....you can take it (the limit tab ) off with a snip or file to allow further adjustment than big brother feels we should have (-;

Man I ripped a tag off a mattress once or twice maybe 3 times lol I'd like to rip this **** off of the saw too, do you know of any videos showing the general procedure? The saw being as new as it is I'm having a hard time tearing into it even though the factory settings are probably more damaging then my tinkering.

 

[MattG]

Man I ripped a tag off a mattress once or twice maybe 3 times lol I'd like to rip this **** off of the saw too, do you know of any videos showing the general procedure? The saw being as new as it is I'm having a hard time tearing into it even though the factory settings are probably more damaging then my tinkering.

Hey John,

I don't know of any such vid. But why don't you upload a piccy here so we can see what you're up against? Might help us advise. For comparison this was the deal on my ms341's carb:


(Sorry bout the lighting level). Anyway, see the top most one? If you look you can see some RED in that rectangular slot on the bottom left quadrant. That's the limiter cap lug....I trimmed this by dipping a v small craft knife in and taking my time. (You could alternatively get a new shaving blade and snap it in half, and use that but FFS be careful...that's the kind of mad stuff I do...). After I'd shaved the lug down I wriggled, pried, and unscrewed those stupid caps with tiny electrical screwdrivers and also tried to lift with tweezers. Eventually I got the b*stads out.

Are yours like this?

 

[olyman]

Your 3120 most likely isn't adjustable on the high side either. I have yet to see a picture of a factory 3120 carb with a h screw.

the older ones did.....

 

[SeMoTony]

I have a few old saw but I wanted newer saws ready to run with safety features, might have went too new nothing but safety and limitations haha

Strongly recommend tuning the saw rich both in the high and low circuit if possible. Getting the saw good and hot while cutting and then letting it idle tuned typically or factory might not be a good idea.

Generally I will set the idle rich enough that it barely stays running after it cools down, very lopey sounding. High side goes as rich as possible while still maintaining the appropriate RPMs loaded during the cut. The Stihl 391s would benefit from a bit more fuel on the idle if your are going to mill with it, also if you are going to mill a lot with that saw(1/2 gallon of fuel plus per milling) try letting it idle while sitting normal, not on the side as though you were still milling with it. Prop it against something and do not just shut it off after making a long cut. It is very easy to heat soak the crap out of a milling saw, may not cause bad immediate damage however could drastically shorten the life of the expensive parts, mostly bearings and everything that gets damaged when bearings go bad in a saw at WOT on its side. Make sure you are pushing on the mill and not the saw.

If your eyes and nose are burning from fumes and your saw is oozing un burnt fuel, might want to back off a bit.

32:1 , 32:1, 32:1, 32:1, 32:1, 32:1....

the older ones did.....

Hey John,

I don't know of any such vid. But why don't you upload a piccy here so we can see what you're up against? Might help us advise. For comparison this was the deal on my ms341's carb:

View attachment 545688
(Sorry bout the lighting level). Anyway, see the top most one? If you look you can see some RED in that rectangular slot on the bottom left quadrant. That's the limiter cap lug....I trimmed this by dipping a v small craft knife in and taking my time. (You could alternatively get a new shaving blade and snap it in half, and use that but FFS be careful...that's the kind of mad stuff I do...). After I'd shaved the lug down I wriggled, pried, and unscrewed those stupid caps with tiny electrical screwdrivers and also tried to lift with tweezers. Eventually I got the b*stads out.

Are yours like this?

Another way is to line up the tab ,after screwing a dry wall screw into that plastic, and pull the plastic bit out. It was easier 4 me to trim the tab outside the carb. I put it back in in case it held the adjustment scrw from vibration altering the tune (-;

 

[olyman]

Another way is to line up the tab ,after screwing a dry wall screw into that plastic, and pull the plastic bit out. It was easier 4 me to trim the tab outside the carb. I put it back in in case it held the adjustment scrw from vibration altering the tune (-;

I was replying to,, the guy that said NO 3120's had the high needle........................

 

[HarleyT]

If this is like other carbs that I have seen, the plate with the green X {2 holes} is just lightly pressed in, and easily pops out.

Then the red caps easily come out.

 

[marti384]

I was replying to,, the guy that said NO 3120's had the high needle........................

I was saying I have never seen any PROOF that some came from the factory with an h needle. Everyone says they were on the first year, but the earliest IPL doesn't show it either. I have always wanted to see a picture of a factory one, to see how they managed to fit it in around the air filter base, since when someone adds a h needle to the existing carb, the filter base needs to be filed down for clearance.

 

[MattG]

the plate with the green X {2 holes} is just lightly pressed in

Yer kidding!! If only I'd known before....would've saved me some aggro

and easily pops out

How did you do that Harley? Just a light spray of slippery stuff and then jimmy it up using 2 little screwdrivers grabbing from the 2 lug slots? Tell us more.

 

[olyman]

I was saying I have never seen any PROOF that some came from the factory with an h needle. Everyone says they were on the first year, but the earliest IPL doesn't show it either. I have always wanted to see a picture of a factory one, to see how they managed to fit it in around the air filter base, since when someone adds a h needle to the existing carb, the filter base needs to be filed down for clearance.

theres a few gents,,who are saw nuts,, in a elsewhere forum, and they said theyve seen em. but no longer own the saws....one is a man of GREAT repute...unlike some others........

 

[John J.]

Finally got the limiters out of my MS391! What a ***** the H-screw was, L was easy, I did it all with the carb in the saw with rear air filter mount loosened but still intact which gave me more access to the L but didn't give me any working room on the high.
I did cut the black screw driver support(?) + pull the limiters off so there goes the warranty and if I have a problem you guys wanna borrow me an unmodded carb? lol

Now I have another issue setting the saw back to factory settings so I'm able to tune (started beautifully before on 1 pull cold sitting for weeks)

Manual states : 3/4 turn out from stop on H...
Is the closed position the same even with limiters installed so I'm not going too far in???

Manual states: 1/4 turn out from stop on L
Same question as above....only 1/4 out from stop that seems lean...are the limiters holding the adjustment between a certain range? Does STOP with a limiter mean needle actually seated? Or Stoped with the tab on the limiter screw???

 

[John J.]

I just got frustrated and cut the damn thing

Yeah the ones on my ms341 were complete turds to remove, they are kinda recessed in a tunnel Used a combination of a small blade (carve off the lugs) and pliers and tweezers and a small screwdriver. Was a really yukky job to do.

I just aligned the notch in the limiter with carb and pulled once I finally got a bite with the pulling screw, I did cut the tab off as well!

 

[MattG]

Finally got the limiters out of my MS391! What a ***** the H-screw was, L was easy, I did it all with the carb in the saw with rear air filter mount loosened but still intact which gave me more access to the L but didn't give me any working room on the high.
I did cut the black screw driver support(?) + pull the limiters off so there goes the warranty and if I have a problem you guys wanna borrow me an unmodded carb? lol

Now I have another issue setting the saw back to factory settings so I'm able to tune (started beautifully before on 1 pull cold sitting for weeks)

Manual states : 3/4 turn out from stop on H...
Is the closed position the same even with limiters installed so I'm not going too far in???

Manual states: 1/4 turn out from stop on L
Same question as above....only 1/4 out from stop that seems lean...are the limiters holding the adjustment between a certain range? Does STOP with a limiter mean needle actually seated? Or Stoped with the tab on the limiter screw???

Glad you got them out John!

No the manual settings will now be inappropriate since the factory set the adjusters at an initial value (I think is it's 1 turn?) and the limiters provide ~3/4 of variation (I think?) around this range.

I probably the best the thing to do is set the H to about 1+1/2, and the L to about 1+1/4 at first (don't overtighten - the threads are quite fine). Tweak the idle screw to get a highish idle to get things up and and running. I now use the manual's (this is from my ms341) proscribed way to fine tune set up the L and idle screws:


A variation of the above will work for a lot of saws. If you don't have a tach then 3,300 is usually just less the than having the chain slowly turned by a slipping clutch. (i.e. increase idle screw till chain catches then back off) and 2800 is a smooth, but lively idle.

I guess the others can help you with the H screw setting.

Hope this helps.....