Stihl MS 390 troubles

[EmannVB]

After much debate and polling here on Forestry Forum, I purchased a new MS 390 about two months ago.  Finally got a chance to put it to work a couple weeks ago, and was less than thrilled.
I was working with a friend, felling 30" Yellow Poplar trees.  On the first cut, the saw seemed to be bogging down.  My buddy had to finish it off with his Husq 350.  I took to limbing and bucking the downed trees, but the saw would contantly stall (restarted 1st pull) and had trouble getting through the log.  Chain was tensioned properly, gas and bar oil were full- it just couldnt cut worth a darn.  I though perhap my mix wasn't exact enough, although my other 4 saws and Stihl weedeater ran fine.  I mixed another can of fuel and tried it the next day.  Same result.  The saw runs and sounds fine out of the wood.  It just can't hold the load when sawing.  I checked the air filter, to make sure it wasnt set for cold weather- it wasn't.  A friend mentioned that it could be the altitude- I bought it in Virginia Beach, and I'm using it at 2800' in WV.  I wouldnt think that would matter at all, but I'm desperate to believe I don't have a bad saw.
Any ideas or things to check?
Thanks,
Mark

[Cut4fun]

After much debate and polling here on Forestry Forum, I purchased a new MS 390 about two months ago.  

You mean somebody here talked you into  a MS390 over a MS361 or MS362  :D :D.  Just joking with you.

I would be taking it back to your dealer to check to see if the carb is set to lean etc first off.  You can make that puppy run in the wind once you are not worried about your warranty with just a muffler mod.  Read the 290 muffler mod thread right in link. https://forestryforum.com/board/index.php/topic,44550.0.html

A 290 can gain 21%-23% quicker cut times with just a muffler mod and carb adjustment.

[EmannVB]

Cut4fun,
I actually took the muffler off and looked it over.  I recalled reading about the muffler mods, but I didn't cut on it just in case I had to take it in. 

Looking over the thread from the arborist website, it looks like a pretty simple mod.  I'm not sure what 4-cycling is though, when talking about increasing the fuel until it "4-cycles". 

~Mark

[John Mc]

I agree with Cut4Fun. The first thing I'd look at is the mixture setting. Seems like everyone is shipping them set very lean these days. It can take a few tanks of fuel run through the saw to get it broken in, but that would not account for the degree of problems you are having.

John Mc

[Al_Smith]

Well I'll tell ya what I would do .Trot that POS back to the dealer and make him fix the dumb thing . I would think it would still be under warentee .

What can happen on an older saw is two things .Either the diaphragm has puckered or the fuel lever is set too low .This certainly shouldn't be the case on a new saw though . I suppose though that a dud could have escaped the factory .It can happen to the best of them which I'm sure was not done on purpose .

I've ran 390's /039's  and for a clamshell they aren't all that bad .

[JohnG28]

What are you running for a bar/chain on it?  If you have a dull chain could be part of the problem, maybe a different, more aggressive chain could help.  I bought a new Stihl in January, and lost the safety chain for full chisel or semi chisel, depending on the cutting, and it does make a didference.  Try turning the H adjustment all the way up (as far out as will go with the retainer).  Thats where mines set till warranty expires.  The other guys are probably right about taking it back though, two months old then needs something, or replacing.  They can even adjust the carb for you.

[SawTroll]

Well I'll tell ya what I would do .Trot that POS back to the dealer and make him fix the dumb thing . I would think it would still be under warentee .
.......

Yes, for once we agree on something   - I guess that at least the "L" is set too lean, when it behaves like this.

Anyway, POS or not; something isn't right - so back to the dealer it should go!

[Al_Smith]

A dull chain won't make them die on the vine .It won't cut worth a hoot though .You ought to be able to put the chain on backwards and it not die like that .

I'll tell you another thing that will screw you up is having the spacer gasket on the wrong side of the diaphragm .Of course one won't think a new saw would have such problems .

[ladylake]

It's just set to lean on the high like a lot of saws now days.   Steve

[joe_indi]

Mark,
If you read the Instruction Manual, you will find that somewhere it mentions that new saws come with their carburetors set a bit rich for them to let them run in better.
It also mentions that the saw runs in by its 15th to 20 tankful of fuel.
After this  the carburetor can to be set leaner.
The manual also mentions something about how the current factory setting  not being the best for a change of altitude. The carb setting would get even richer.
All this could cause your new saw to stall or bog down.
So you might need to adjust the carburetor.

(You will need the guide bar and chain to be fitted for the next couple of steps.
Preferably, you should do this at the altitude that you are using the saw.)

To verify this, start up the saw, while it is running at full throttle, tap the brake on and at the same time release the throttle.
The engine should not stall at idle.
If it stalls it is running too rich.
Lean out the idle by turning the L screw clockwise in 2 minute increments till the engine idles without stalling.
You might have to ease out the idle screw (the one below) a bit because the leaning of the L screw will cause the idle speed to increase.
Once you have the idle setting right, with the screwdriver in the slot of the H screw go to full throttle.
Lean out  the H screw clockwise till it stops 4 stroking (sputtering at high speed).
Ease off the throttle completely for a couple of seconds and then go to full throttle again and ease the H screw anti clockwise till the 4 stroking just begins.Continue turning it out another quarter turn.
Try the saw in the wood now it should run fine.
Dont forget to reset the carb when you go back to a lower altitude.

Joe

[ladylake]

Joe  Since the EPA got involved over here a lot of saws come set to lean to keep the emmisions down and it only get worse with ethonal gas.  His saw sounds to lean by the description he gave, bogs easy in the cut but runs fine out of the cut.   Stevwe

[SawTroll]

Joe  Since the EPA got involved over here a lot of saws come set to lean to keep the emmisions down and it only get worse with ethonal gas.  His saw sounds to lean by the description he gave, bogs easy in the cut but runs fine out of the cut.   Stevwe

This time I agree with you as well!   ;D

US market "special" though, not a world-wide rule. :

[Warren]

EVB,

I've been running an MS390 for the past 3 or 4 years with a 24" bar and 3/8 chisel chain, with zero problems. Take it back to the dealer and have them test it / tune it / make it right....

-w-

[EmannVB]

Joe,

Thanks for the detailed instructions! 

:D Now about this ..."read the instructions...." business:  I'm a man, I know everything by virtue of being  a man.  Instructions are for girly-men who drive foreign cars to the "office".  Us men of the wood have no time for hinderances of instruction manuals!!!
I'll read it as soon as my wife's not watching...  :P