Stihl ms360 leans out on top end.

[Nate.]

I’ve got an issue with my dad’s ms360. Saw runs the way it should except when I pin it wide open. It will 4 stroke normally for 2-3 seconds then lean out and start screaming. Anyone run into this? Thought I’d check with you guys before I start pulling it apart.

Best Regards, Nathan

 

[drf256]

It happens often. it’s usually the carb. Have to check tank vent, fuel line and filter, and rebuild carb. Check carb popoff as well.

 

[hacskaroly]

It will 4 stroke normally for 2-3 seconds then lean out and start screaming. Anyone run into this?

I would lean towards intermittent air leak, once it gets going then the leak opens up. Possibly one of the oil seals.

Edit, on second thought, go with @drf256 's prognosis first.

 

[Nate.]

Copy, I’ll go after the fuel system & see what turns up.

 

[Coupe]

I was always told that when ajusting the carb on a 2 stroke take them till they are screaming
on your high jet then back them off a bit till they just 4 stroke a bit. could be wrong on that though.

 

[Wonkydonkey]

Not that you have the same problem as I did.

Saw ran fin in the morning (200t) small cuts etc.
Then started screaming like as it was starting to run out of fuel. However the tank was half full.
I thought tank vent first , so i popped the fuel cap and popped it a few times again. When it started to scream.

I tried to tune it but it screamed after 5sec of running ok.
For some reason I thought maybe a pin hole in fuel line ( in tank ) so I refilled the tank and it ran fine.. well until about half the tank was empty

Turned out to be the tank fuel filter sucking air at the fuel hose connection @ about half a tank

Any ways does sound like fuel and air then leaning out . It’s just finding it

Btw I had a 260 which did something similar except it did matter if the tank was full. It was the impulse line.

 

[Wonkydonkey]

Not that you have the same problem as I did.

Saw ran fin in the morning (200t) small cuts etc.
Then started screaming like as it was starting to run out of fuel. However the tank was half full.
I thought tank vent first , so i popped the fuel cap and popped it a few times again. When it started to scream.

I tried to tune it but it screamed after 5sec of running ok.
For some reason I thought maybe a pin hole in fuel line ( in tank ) so I refilled the tank and it ran fine.. well until about half the tank was empty

Turned out to be the tank fuel filter sucking air at the fuel hose connection @ about half a tank

Any ways does sound like fuel and air then leaning out . It’s just finding it

Btw I had a 260 which didsomething similar except it didn't matter if the tank was full. It was the impulse line.

Hopefully it’s easy and not apita to find..

 

[Nate.]

I can richen the saw down to like 10k rpm and it will still start screaming after a couple seconds at wot. My first thought would be fuel line but it’s brand new along with the fuel filter so I think I’ll go for a carb tune up.

 

[Coupe]

Might have to give it a preasure test, sounds as it could be sucking air in.

 

[hacskaroly]

so I think I’ll go for a carb tune up.

Might be sucking in air past the carb but before the cylinder or like Wonkey said possibly with the impulse line.

 

[Canadian farm boy]

Micro screen in the carb could be plugged up. Carb kit should come with a new screen.

 

[Nate.]

it does seem to me like it runs outa fuel at the top end…

 

[huskihl]

I can richen the saw down to like 10k rpm and it will still start screaming after a couple seconds at wot. My first thought would be fuel line but it’s brand new along with the fuel filter so I think I’ll go for a carb tune up.

Any saw I’ve ever had that revved to the screw settings and then takes off and screams needed crank seals. They will hold for a few seconds but as the engine revs up it’s looking for more air.

 

[pbillyi69]

my 046 did that and i chased it for weeks because it didnt do it all the time.....it was the crank seal on the clutch side.....it was a pain to figure out i tried everything and was convinced that there was a pinhole in the carb boot. when i got the boot off and didnt find a hole. i took it to a shop for pressure testing. which it passed but failed the vac test. that was before i had any of the tools for checking myself

 

[Jimmy in NC]

Also do not look over the fuel tank pick up filter. I've had those be restricted and do exactly like you say. I'll try to find the video I had of it.

 

[Jimmy in NC]

Here is a video of an 066 doong this...was simply the pickup.

 

[Nate.]

Appreciate the answers guys! I will pressure/vac test it when I get the carb off. The in tank fuel filter is new along with the fuel line. Crank seals are a very real possibility as this is a high hour saw that’s been run hard and rarely maintained.

 

[Nate.]

Here is a video of an 066 doong this...was simply the pickup.

That is exactly what this saw does!

 

[Nate.]

Alright, here is the update from today! Pulled carb & cleaned it, everything looked okay inside. Pulled and replaced both crank seals because they felt brittle even though it held pressure/vac. The problem persisted so I finally swapped an old carb on that has a very touchy low speed needle. The saw didn’t idle great but the issue is gone and it held steady top end rpm. I’m gonna order a kit and see if I can find the culprit inside that carb. Appreciate the reply’s and help!

 

[Coupe]

Make sure you give the carby that's causing you all the headaches a really good solid clean.
I would beg,borrow or steal an ultrasonic cleaner and give it a dose of that.
By the sound of what you have said it most certainly is pointing at that carb. Good
luck and hope you get to the bottom of it.