Stihl MS361 dies mid range (Australia) - help!

[Scratcho]

Hi guys. I’m new to the forum and have joined to get advice on a problem with a Stihl chainsaw. I have 3 chainsaws: An old Stihl MS290, a Husky 445E, and a Stihl MS361. We live on a property at Bellthorpe (Australia) with lots of forest, fallen timber and trees, and firewood to cut etc, so there’s always plenty of work for the chainsaws.

The 361 used to belong to my elderly father in law and he gave it to me as he’s now too old to use it and now lives in the city. It hasn’t done a lot of work, and it was working perfectly a few days ago. A ripper of a saw. Then suddenly it began misbehaving. It starts fine using the usual method (hold trigger in, push lever to bottom for choke, pull till fires, click lever up one notch then pull till starts). It runs well for about 5 seconds then it starts to die as you give it some revs, and proceeds to die entirely. If you can coax it up to near maximum revs, it seems to run well and cut with normal power but if you let the revs drop, it will start to die again. If you go through the cold-start procedure again it starts again but same scenario. I’ve put a new plug in, the air filter’s good. It has no spark arrestor (I removed the muffler and checked). I’ve played with the “L” mixture screw and it made no difference. I pulled the carb off to see if there was anything obvious, but wasn’t brave enough to open up the carb.

Any suggestions/ advice?

 

[trooney]

Has anyone done a pressure and vac check on it? Thats where I would start. Welcome to the site. Stick around, we got some real knowledgeable people in here....and some that like to push buttons!! Lol

 

[Scratcho]

Thanks. No, I'm fearful that if I take it to a shop, they'll tell me to leave it with them and I'll get a $200 bill when I pick it up. I'm out of town so it's about 40 mins to a small engine shop.

 

[Wood Doctor]

Seems like s fuel issue. Start first by replacing the fuel filter (pickup body). If that fails, the carb likely needs to be replaced or rebuilt. Regardless, replace that fuel filter first and then report back.

 

[czar800]

Welcome to the forum, What you’re describing sounds like a air leak. The most likely air leaks are Crank seals, impulse hoses, intake boots and base gaskets to name a few.
As said above a pressure test will be the best starting point to find your your problem. I’d also check over the fuel system including inside in the tank and where it’s going through the tank. Of course don’t forget cleaning and rebuilding the carburetor.

 

[Big_6]

It sounds like a bad diaphragm. Get a new carb or rebuild it for cheap!
Don't discount the fact there might be an air leak.

Sent from my SM-N975U using Tapatalk

 

[Czed]

Hi guys. I’m new to the forum and have joined to get advice on a problem with a Stihl chainsaw. I have 3 chainsaws: An old Stihl MS290, a Husky 445E, and a Stihl MS361. We live on a property at Bellthorpe (Australia) with lots of forest, fallen timber and trees, and firewood to cut etc, so there’s always plenty of work for the chainsaws.

The 361 used to belong to my elderly father in law and he gave it to me as he’s now too old to use it and now lives in the city. It hasn’t done a lot of work, and it was working perfectly a few days ago. A ripper of a saw. Then suddenly it began misbehaving. It starts fine using the usual method (hold trigger in, push lever to bottom for choke, pull till fires, click lever up one notch then pull till starts). It runs well for about 5 seconds then it starts to die as you give it some revs, and proceeds to die entirely. If you can coax it up to near maximum revs, it seems to run well and cut with normal power but if you let the revs drop, it will start to die again. If you go through the cold-start procedure again it starts again but same scenario. I’ve put a new plug in, the air filter’s good. It has no spark arrestor (I removed the muffler and checked). I’ve played with the “L” mixture screw and it made no difference. I pulled the carb off to see if there was anything obvious, but wasn’t brave enough to open up the carb.

Any suggestions/ advice?

Welcome to the site
Check your fuel and impulse line's
For cracks
And if they hold dimensions without collapsing.
Especially check inside the tank.
A carb rebuild is next and easy
If it's crank seals
They are not bad too do.

 

[Scratcho]

Thanks for the info guys - although I'm not bad at mechanical stuff, at the moment, the suggestions might involve stuff that I don't have the knowledge for, or requires equipment that I don't have. Do you need a special tool to do the air leak/ vacuum check? And how do you do it? Is there a link for a video or whatever on rebuilding the carb, and how to check the diaphragm? Thanks!

 

[Wood Doctor]

Scratcho said, "It runs well for about 5 seconds then it starts to die as you give it some revs, and proceeds to die entirely. If you can coax it up to near maximum revs, it seems to run well and cut with normal power but if you let the revs drop, it will start to die again. If you go through the cold-start procedure again it starts again but same scenario."
-----------------
Still sounds like a fuel filter/issue problem to me. Let it sit for awhile and it will start again but then die on you as if it were running out of fuel. Right? No special tools are required to change out the fuel filter and check for improvement.

 

[jmester]

Those 361 with Hd-34 carbs have accelerator pumps. That can leak air and cause a lean conditions. Sounds like a fuel issue to me as well. Also have a look at the fuel line. Maybe cracked or have a hole in the line.

I would hate to see you just throw parts at it. Hoping to fix a problem. I would want to at least pressure test the carb and see if its leaking.

The diagrams will become stiff and hard over time. That causes issues.

 

[Scratcho]

The reason I don't think it's the fuel filter is that if you can coax it up past the midrange, it will run flat out on full throttle full power and cut normally. I would have thought that a restriction to fuel flow would prevent it from running at full throttle, where the fuel demand is a lot higher. Does that logic work? I have plenty of experience with carburettor jetting on 2 stroke bikes, but not with these chainsaw small engines with their amazing little compact carbies!

 

[trooney]

The reason I don't think it's the fuel filter is that if you can coax it up past the midrange, it will run flat out on full throttle full power and cut normally. I would have thought that a restriction to fuel flow would prevent it from running at full throttle, where the fuel demand is a lot higher. Does that logic work? I have plenty of experience with carburettor jetting on 2 stroke bikes, but not with these chainsaw small engines with their amazing little compact carbies!

Thats what I was thinking too. Had a couple of saws do it to me. Thats why I suggested a p&v test. That at least will eliminate or confirm an air leak. Then if its not, then move on to next. OP, there must be somebody in OZ that will help you out. Its not hard to do, but if you're like me you like to be shown first. It might be worth your time to bring it to a reputable shop.

 

[jacob j.]

It sounds like you have cracked impulse line. Take a look at the IPL, page 21, #20:

 

[trooney]

Its no. 20 under the tank handle...

 

[Scratcho]

OK great, thanks, I'll have a look. Thanks very much for posting that pdf.

 

[czar800]

I just had a G366 (China ms361) acting very similar on my bench. It ended up being the flywheel side seal leaking.
I block off the exhaust and carburetor and use a old compression tester hose threaded in for my pressure/vac testing.

 

[czar800]

I almost always dunk the saw in a soapy water bath to find out what’s leaking. Sometimes I can just locate leaks with a spray bottle, but it’s easier for me to dunk it and get it over with.
I’m lucky I have a sink in my shop now, but before I used a storage bin filled with water.
Just don’t pull a vacuum test...

 

[Scratcho]

I think you have mechanical skills more advanced than I. Or at least, more confidence in stripping down the saw. I did strip down the MS290 years ago after I dropped a tree branch on it, breaking the exhaust flange and I had to replace the cylinder. But it was a big job. I don't know where to start with this one and I don't have things like a compression tester to adapt.

I've flushed out the fuel tank, changed the fuel filter, put in a new plug and air filter, removed both covers off the carb body (diaphragm looks a bit stretched but good otherwise, no holes) and I've blown all the ports with an air jet. Still the same, or worse. I've turned the mixture screws various ways. No luck. I think I'm going to end up taking it to the small engine shop tomorrow.

I did a short vid of what it does when I start it. It's got worse - I used to be able to keep it running if I coaxed it but now, soon as it's burnt the choke drawn fuel, it dies immediately and completely.

 

[Kiwioilboiler]

I think you have mechanical skills more advanced than I. Or at least, more confidence in stripping down the saw. I did strip down the MS290 years ago after I dropped a tree branch on it, breaking the exhaust flange and I had to replace the cylinder. But it was a big job. I don't know where to start with this one and I don't have things like a compression tester to adapt.

I've flushed out the fuel tank, changed the fuel filter, put in a new plug and air filter, removed both covers off the carb body (diaphragm looks a bit stretched but good otherwise, no holes) and I've blown all the ports with an air jet. Still the same, or worse. I've turned the mixture screws various ways. No luck. I think I'm going to end up taking it to the small engine shop tomorrow.

I did a short vid of what it does when I start it. It's got worse - I used to be able to keep it running if I coaxed it but now, soon as it's burnt the choke drawn fuel, it dies immediately and completely.

Don't wuss out, that's not the Australasian way!

It's a chainsaw mate. They are not that complicated even though they can be frustrating. If you can calmly work out how to get to the impulse hose that supplies the crank suckNblow to the carburettor (effectively the fuel pump) then I reckon you should do that and check that impulse hose for a crack somewhere along it's length.
Why? Because I had an 024 that exhibited very similar behaviour as you are experiencing now, and that's what it was.
If you are remote the ability to suss this stuff is gonna be very handy instead of 'run to town'.

 

[Scratcho]

OK you mad Kiwi, you're right, I'll have another crack. I mean, we're not as good as the Kiwis for just gettin' stuff done, but we're not hopeless!! Cheers.