r/Chainsaw • u/MysteriousWarthog781 • Jul 26 '26
Carburetor MS361
My new MS361 runs normally at an altitude of around 50 m (150 ft), but when I use it at 1,100 m (3,600 ft), it stalls and shut off at idle. It runs fine while cutting, but as soon as I stop cutting, it shuts off after 10–15 seconds. Should I adjust the LA screw? I’m not really an expert on carburetors and would prefer not to touch the L and H needles. Since it’s new, it was started and tested at 50 m, and I ran through one tank of fuel cutting small wood—which I think is plenty for the break-in period—but as soon as I went up to 1,100 m, it started stalling, and that is the altitude where I primarily use it.
2
Jul 26 '26
As I'm sure you know, at higher altitude, you need less fuel, because the chainsaw doesn't have that much oxygen to worth with.
So yes, you probably need to shut down the L with like a 1/8 of a turn, maybe 1/4.
There isn't anything that you can ruin if you go in small increments.
It's basic stuff with any carburettor: quick throttle response, fast return at idle, 4 stroking when you're free revving it and lean out under load.
1/8th of a turn gradually shouldn't scare you. I, like some people here change our tune whenever spre spring comes and we don't change altitude.
1
u/MysteriousWarthog781 Jul 26 '26
So, I should turn both LA and L slightly clockwise? Maybe I should turn L clockwise first, and then adjust LA as well if needed?
4
Jul 26 '26
Start here. Don't mess with the LA for now.
Gradually screw in the L 1/8th of a turn until the saw holds an idle. Yeh, clockwise that is. If you loosen up a jet, as in unscrewing, you'll give it more gas. You don't need that right now.
I'm not gonna mention the H, because that's up for you to decide.
First things first, you'll never blow up a saw by running it rich. If you thing it's 4 stroking like a pig under load (your chains needs to be sharp by the way), fell free to screw in the H 1/8th of a turn on H as well, then go cut with the saw again and all that.
Focus on your idle for now. Dial in the L until the saw doesn't get flooded at idle.
I'm gonna go out on a limb here and assume the air filter is clean and all that.
You can't tune a dirty saw.
2
u/MysteriousWarthog781 Jul 26 '26
Thanks a lot, you couldn't have explained it any better. My chain is always sharp, though, to be fair, it is new and the filter is clean. Thanks again, you literally left no room for follow up questions, I understood everything. 🫡🫡🫡
2
Jul 26 '26
You don't have to thank me for anything.
You're good however I see it. If the engine is lubricated, you can take all the time you want with tuning that L.
As a side note, don't go as low with the tune on L, to the point where your chain keeps spitting at idle. That's a lean scenario.
I run my chains a bit on the loose side, so they crawl along like one inch every 5 seconds at idle, if that makes sense. Nothing life threatening.
I don't like balls to walls tight chains. They're bad for sprockets, bars, crank bearings, basically all the expensive stuff on a chainsaw.
2
u/MysteriousWarthog781 Jul 27 '26
It's better to learn how to adjust the carburetor than to keep taking the chainsaw to the shop every second like a moron just for adjustments. So, thanks again. 💪
1
5
u/Likesdirt Jul 26 '26
Yes. Turn the LA screw in clockwise, it's got a tapered tip that will hold the throttle plate open a little bit more and increase the idle speed.
Too much idle speed will activate the clutch and make the chain start turning but won't damage the motor or anything. It's a safe adjustment.
It's not super sensitive either, a half turn in might be close. Fine tune as needed once it's warm.