Adjusting H screw only for milling/ General tuning questions

[John J.]

I get the basics of tuning a saw and I'm still learning, I have a new Ms391 just broken in I've been using it for milling small logs and plan to use my 3120xp for large ones. My question is can I slightly increase the high screw for a little extra 4-stroking at WOT W/O changing idle and L screw? Or do I need to go through the whole tuning procedure??

Also saw this in the owners manual:

Fine tuning for operation at high altitude
A slight correction of the setting may be necessary if engine does not run satisfactorily:
N Carry out the standard setting. N Warm up the engine.
N Turn high speed screw (H) slightly clockwise (leaner) – no further than stop.
NOTICE
After returning from high altitude, reset

Just out of curiosity less oxygen at higher altitude these adjustments are recommended to keep the saw from running overly rich?

 

[Andyshine77]

When adjusting for milling, you normally can get away with just adjusting the H. When tuning for milling you want the saw to just stop 4 stroking while cutting. As the saw heats up you may have to adjust the carb a few times. Running more oil while milling is also recommended.

Whenever you change altitude, or when the temperature changes, you'll need to adjust the air fuel ratio to compensate for the change in air density.

 

[MattG]

When adjusting for milling, you normally can get away with just adjusting the H. When tuning for milling you want the saw to just stop 4 stroking while cutting. As the saw heats up you may have to adjust the carb a few times. Running more oil while milling is also recommended.

Whenever you change altitude, or when the temperature changes, you'll need to adjust the air fuel ratio to compensate for the change in air density.

I don't do milling so this is just for curiosity re. tuning in general.

So am I right in saying that as a saw heats up through out working time, it's beneficial for the mixture to be v. slightly richer to assist cooling further and hence better engine wear and performance characteristics generally?

I'm curious since although I like my saws to be as powerful (lean?) as is safe for good cutting of firewood, I've also noticed that sometimes when I'm going through a big log for the saw, that it can start to "fade" a bit as if it's overheating, and after such a cut I sometimes hear the muffler "ticking" from the heat, presumably, like you sometimes do on car.

 

[John J.]

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!

 

[Andyshine77]

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!

Yes the screw has a limiter on it, and it must be deleted for full adjustment.

 

[John J.]

Yes the screw has a limiter on it, and it must be deleted for full adjustment.

How do you delete this?

 

[Stihl working hard]

Just be aware you may void your new saw warranty if you remove the limiter caps .in saying that you can get a limiter removal tool to remove them giving you a full range of adjustment.You can get the tool from Stihl .

 

[earlthegoat2]

I would not mill with any saw that still has limit caps on them unless you truly are not stressing the saw with a large cut. I would think any milling would stress a 391 pretty good.

50:1 mix cools the saw better than 42:1 or 30:1. 50:1 lubricates fine so there is little reason to go with a higher oil mix. Heat is the big problem with milling, not internal engine lubrication. Richer tuning cools the saw better too. As was mentioned above, tuning the sa just so it doesn't 4 stroke in the cut is a good rule.

 

[Andyshine77]

I would not mill with any saw that still has limit caps on them unless you truly are not stressing the saw with a large cut. I would think any milling would stress a 391 pretty good.

50:1 mix cools the saw better than 42:1 or 30:1. 50:1 lubricates fine so there is little reason to go with a higher oil mix. Heat is the big problem with milling, not internal engine lubrication. Richer tuning cools the saw better too. As was mentioned above, tuning the sa just so it doesn't 4 stroke in the cut is a good rule.

The documented change in temperature between 32:1 and 50:1 is essentially not measurable. The added benefits of more oil far outweighs any negatives, even 16:1 is fine. It's all In the tuning.

 

[Andyshine77]

I don't do milling so this is just for curiosity re. tuning in general.

So am I right in saying that as a saw heats up through out working time, it's beneficial for the mixture to be v. slightly richer to assist cooling further and hence better engine wear and performance characteristics generally?

I'm curious since although I like my saws to be as powerful (lean?) as is safe for good cutting of firewood, I've also noticed that sometimes when I'm going through a big log for the saw, that it can start to "fade" a bit as if it's overheating, and after such a cut I sometimes hear the muffler "ticking" from the heat, presumably, like you sometimes do on car.

The saw has to be tuned for the application, if you're constantly cutting large rounds you have to tune a bit more rich. Allowing the saw to cut without pushing much helps as well. Wouldn't worry about the ticking noise too much, the exhausts on saws can get quite hot during prolonged cuts.

 

[Stihl working hard]

The documented change in temperature between 32:1 and 50:1 is essentially not measurable. The added benefits of more oil far outweighs any negatives, even 16:1 is fine. It's all In the tuning.

I personally wouldn't mill with a clamshell saw way to much stress on the saw, lubrication is the key hear as well as heat dispersion 32:1 is my preferred ratio for all my saws ported or stock 50:1 is to lean I have built enough saws and seen what 50:1 does to main bearings it leaves them dry and offers premature wear just my 2 cents worth

 

[blsnelling]

Milling with less than 32:1 is plain foolish, IMHO. I wouldn't consider milling with a saw with the limiters not trimmed either. There's no way that it can be tuned rich enough for that application.

 

[earlthegoat2]

This question might be better asked in the milling section as well. There are folks there who have milled thousands of b/f of lumber and have put countless hours on saws set up specifically for milling.

An oil mix war in the milling forum would be a little bit more legit as to the content of this post than the folks here who have merely dabbled in it.

 

[Bmezz88]

have fun getting those limiter caps off that saw... I just yanked them off of my 391 and it was a pain. there is this little plastic piece in front of the limiters that won't allow them to get through. I just cut it off lol

 

[blsnelling]

Line up the tab with the slot, screw in a wood screw, and it'll pull right out. Trim the limiting tab and re-install.

 

[Bmezz88]

I did just that. heres a pic of that piece. it tappers down on the backside.

 

[Bmezz88]

I just got frustrated and cut the damn thing

 

[MattG]

have fun getting those limiter caps off that saw... I just yanked them off of my 391 and it was a pain. there is this little plastic piece in front of the limiters that won't allow them to get through. I just cut it off lol

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.

 

[earlthegoat2]

I know they are pretty difficult on the 291/311/391 series. All the more reason not to mill with these series of saws.

 

[Mad Professor]

The documented change in temperature between 32:1 and 50:1 is essentially not measurable. The added benefits of more oil far outweighs any negatives, even 16:1 is fine. It's all In the tuning.

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