MS 391 Not Starting

[Sam R]

Justin yeah, I don't spend a lot of time in the field - you see I'm just a shop mechanic for a Stihl dealer. I wonder though, how well does your method work? I guess w/ the plug out & no compression your fuel pump won't pump much fuel. I consider myself an eternal student of the 2 stroke engine and I like all the interesting answers for problems people come up with on here.

 

[Sam R]

Chipper yeah, I don't consider myself a master mechanic by any stretch but I am very thorough with regards to repairs & diagnosis. My hope is that people can bring their OPE to us and get good service, solid repairs and a good experience. We'll see how it goes though. Like your tag line there says, I'm working to learn.

 

[pavel408]

For starting a flooded saw, my dealer (HQ+Echo) advised me the same procedure as Justin posted.

 

[JustinSL]

Justin yeah, I don't spend a lot of time in the field - you see I'm just a shop mechanic for a Stihl dealer. I wonder though, how well does your method work? I guess w/ the plug out & no compression your fuel pump won't pump much fuel. I consider myself an eternal student of the 2 stroke engine and I like all the interesting answers for problems people come up with on here.

It works I have tried it. Sometimes it takes a few pulls but it will start.

 

[JustinSL]

Chipper yeah, I don't consider myself a master mechanic by any stretch but I am very thorough with regards to repairs & diagnosis. My hope is that people can bring their *** to us and get good service, solid repairs and a good experience. We'll see how it goes though. Like your tag line there says, I'm working to learn.

I wish my local shops had guys like you that want to do the work and take pride in it. I’m fairly mechanically inclined but I hate to say it but I know more about the product than most of the local shops. I do run saws and other power tools and enjoy them a lot and like to learn. I have a friend that used to be a mechanic in a Stihl and Husqvarna shop for a few years and usually I can call him and either take it to him or he can help me through it.

 

[Sam R]

Man I look forward to every day I can spend at the shop. I learn so much and love it when I can get someone back to work whether It's light hard work or a pro needing to get paid.
Also don't know why I got censored, it said O P E.
Hopefully after some time people talk about our shop like we know what we're doing. I know there are 2 other Stihl dealers in town here one is completely useless the other, their mechanic has given me dubious advice before.
Hopefully this 391 doesn't come back, but once I got it tuned up and minor carb adjustment it seemed good. I did tell the owner that since I had to adjust the carb a bit it'll probably need the carb cleaned or replaced before too long but this got him sawing for about $30.

 

[Jweslock]

Hey folks,

I've got a 391 in the shop right now that came in with complaint of won't start.
Been through the diagnosis; checked it from top to bottom. Good spark, tank vent works, tank holds pressure, fuel lines good no cracks or leaks. Good spark, even put a new plug. Torched the spark arrester even though it looked pretty clear. P/v test was good, .5 bar for at least 20 sec.
Air filter looks good, fuel filter in it was too big. I didn't have the exact one so I put a 0000 350 3502 which is similar.
I even swapped the carb & comp valve for new. Also reset magneto air gap to spec. Made sure the chain brake was disengaged.

It just won't fire up. Got it to start for a minute when I started fiddling with it before I did anything it ran rough and smoked a lot. Would not restart after.
And once in my diagnosis it fired up for a couple seconds when I had the ZAT4 on it. Died. Sounded like from running out of gas.
Also put fresh Motomix in it.
I need some ideas. At this point I'm stumped.

One other thing, I took the spark plug out, muffler confirms that it's getting some gas. There was a fine mist in combustion chamber and muffler was wet inside.
Also compression is good as verified by drop test w/ deco valve engaged.
I'm thinking maybe I flooded it and I'll try again after lunch here. But I've never had a saw be this hard to start that didn't have a bad carb or serious air leak.

Thanks folks

It’s a piece of crap… I have one and have spent more time trying to get it to start than using it. This Stihl is a piece of garbage. Breaking it apart for parts.

 

[dmb2613]

You have to have knowledge to start a saw, all Stihls flood EZ