Stihl ms391 review and starting tips

[prsv07]

I just got a new ms391. It is a great saw.  It starts quite easily if you do it properly ,and it really does go through the wood in a hurry.  I cut down and processed a fair sized , dead, seasoned elm , which is pretty hard wood.   It was a pleasure to see how fast the big trunk was reduced to fireplace length pieces.  Stihl highly recommends using the green chains, but my 391 came with the yellow chain.   It worked fine for me and cut very fast. 

Regarding hard starting on Stihl chainsaws-  you can probably read this same info in other places, but anyway I hope this helps...
1. use fresh gasoline that has the proper oil mix.

2. don't pull the start rope too many times with full choke.   Once flooded it is a problem.  Just pull the starter  with full choke until you hear the little "pop" sound, then switch to the fast idle setting for the next pull.  My 391 will actually fire up and run briefly on full choke.

3.  When finished working for the day, make sure to run the saw until "dry" ( all the fuel in the carb and line is used up).  Do NOT store the saw for a long time with fuel mix in the carb and lines.  That just about makes it impossible to start if you wait a long time before trying.

4. My Stihl dealer says that ethanol gasoline(10%) is OK as long as it is fresh and you don't store the saw without running it dry first.   I have found this to be be valid information with my ms250 and ms391.

Numbers 1,2,and 3 above are all of equal importance.

[Southside]

Does the 391 have a fuel shut off or something so you can run it dry?  I would be concerned about scoring the piston doing that. 

[Jason S]

Have had the same saw for a couple years. While I like it, it is NOT a pro model saw.  But that said around my "farm", it does real well. It is a little underpowered with a 28" bar it does fine with a 20 & 25. But there are a lot of saws that will sling a 20" bar as well and weigh way less. But frequently I use it for felling fairly large Doug Fir and WRC's.

Reason I posted is the run it out of gas comment. I know it is expensive, but I store my saws locked, cocked and ready to rock. As such Stihl Motomix is used on my next to last, last tank, and fill up to store tank of the day. Saw will rock to life on just a couple pulls, idle great and purr like 10% ethanol never will. Why risk gumming the carb and deteriorating fuel lines if you don't have too. Even running it out residual will remain in the lines and attract moisture.  If I am running all day for several days i will run blend, but for occasional use the Motomix pays for itself in a lack of repairs. I can let the saw sit for two months and it will rock

Just my 2 cents. I never run them dry, any of my 2 cycle stuff.

Guess I just like my saws like I like my 45's. Nothing like having to fill fuel and bar oil feeding horses at 4 AM in the morning before work.

[prsv07]

To run the saw "dry" means to run until there is no liquid fuel in the carb or fuel line.  There is no shutoff valve, : 1. pour all the fuel from the tank  2. start the saw and let it run until it stops from fuel starvation.   If the fuel has the proper oil mixture, there will be no damage to the cylinder.   This method is recommended by Stihl dealers.

[prsv07]

sorry, I meant to say, "no damage to the piston"

[Ianab]

Leaving old fuel in them will cause more problems than running them dry is going to.

Yes it's going to run lean for 1/2 a second, but it's not under power, and it's not long enough to heat anything up or run out of lube.

Only time I have trouble with my ms310 (similar saw) is if I can't decide if it's a cold start or a warm start, and end up flooding it with too much choke. Cold it starts fine with the method prsv07 suggests. Warm it starts fine just setting it to fast idle and no choke.  It's in between. I've found if It wont start when I think it should be warm, just one pull with choke, then set the fast idle and fires up fine.

[prsv07]

I certainly don't disagree with Jason S, but  I have read of many  guys having trouble starting their saws after they DID leave ethanol-gasoline in their machines for a long time.   Anyway...  running out all the fuel and using fresh mixed fuel the next time I start it works fine for me.  I live in Dallas, and all available gasoline has ethanol.  If I can get by without paying 7 bucks a quart for premix fuel,  I will. 

By the way- I didn't mention warm starts on my ms391 because it starts so easily. It starts immediately on slow idle with one pull when warm.  no choke needed

[Southside]

Good to know - if I can ever get to the point where my saws sit for any length of time I will keep this in mind for sure. 

[Scruboak]

Just so im clear on this...i have 91 non ethanol fuel avilable everywhere here and i run it in the Harley the saw the lawnmower and everything. So i can leave the saw sit for few months and no worries?? Stihl dealer said run their motomix in the last tank if i know im not going to use it for a bit

[ladylake]

 The trouble with running them until out of fuel is that some fuel will remain in the carb and gunk up for sure.  Steve

[prsv07]

Reply to Scruboak-
I just saw your reply to my post about ms391 starting tips.   From what I can tell, the main reason for the existence of premix fuel is the presence of ethanol in most pump gasoline.   If you have ethanol free gasoline in your area and use Stihl oil,  then you should have no need of the Stihl motomix.  I have no information on how long you can leave motomix in a saw, but you can find out for yourself.  If your Stihl dealer recommends it ... go for it.   My local Stihl dealer advises that even with our ethanol laced gasoline,  I will have no problems if I just use fresh gasoline and run the saw dry after using it.

We know that  gasoline is very volatile.  From my experience,  when trying to start an engine that has been sitting idle for a long time,   the FIRST thing to do is put fresh gasoline in it.   Maybe the Stihl premix is specifically made to store for a long time.    Of course this depends on how long is long.   If it is several months , I suspect that either the "run dry" method  or the "storage with motomix" method would both work.    If long means several years,I wouldn't want to leave any kind of fuel in the saw.  I would probably disassemble the carb , clean with  toluol, and reassemble,  before storage.

Anyway, those are my thoughts.   Hope it helps.
PRS