Stihl MS391 - hanging idle diagnosis & muffler mod

This MS391 had a "hanging idle" that had me rather stumped for a while, but we got 'er licked! Muffler mod didn't show HUGE gains in "cut time," but it held better rpm in the cut. It was breathing better, and certainly kicked up the throttle response a solid bit. Throttle response was my main goal with the mod on this saw.

[@alandavis8892]

Ridiculously awesome video. Well in depth and very informative thanks so much was much needed for mine!

[@johndepweg4029]

I have been having the exact same hanging idle in my 391. Thank you for the video

[@VincesDIYs]

Have not seen you in awhile. Congrats on the 1k subscribers!

[@crazyfeller5704]

That was a great video. Well done! Good humor man looks to be happy now.

[@ruggedtimber1743]

Hey Ben, Great video. Glad you were able to figure out the carb issues. Once again very informative. Love the Billy Lacount t-shirt. Tell him he should sell them. Stay safe.

[@samishsawworks5870]

Pretty sure I could make a t-shirt sale happen ;) if nothing else I could sell you mine......... it's already "worn in" haha. Shoot me an email [e-mail] and we'll get you hooked up. They're super comfy and fit great.

[@ruggedtimber1743]

@@samishsawworks5870 thanks. Sent you an email.

[@zukiryder4006]

Hey Ben! Good to see ya again.

[@simpleman4224]

You will figure it out! I have no doubt! Good seeing ya buddy! 👍👍👍👍🇺🇸🇺🇸🇺🇸🇺🇸🙏🙏🙏🙏

[@barnyardbrio7597]

excellent tutorial!!! so many people (most) own saws and do not know how to take care of them. and their saws do not run right because of this.

[@scotthomberg141]

Awesome! Was thinking about doing this to my 291.

[@samishsawworks5870]

It's definitely worth the time invested in my opinion.

[@sdranch2800]

Exactly why I only use the Stihl pre mix fuel, yes it costs more than mixing my own. But I don’t have to pay for new carbs and troubleshooting when someone mixes the fuel wrong, or uses ethanol fuel cause they didn’t want to drive as far to the station with non ethanol ect. A little more up front saves a lot of headache and down time.

[@DaveyBlue32]

Needs the Hyway popup piston! Those quad lower transfers are dying to get opened up they are ugly from the factory… I open and polish the exhaust port window and I open the intake port window too… I usually roll around in those upper transfer’s to give them a little more flow… with that Hyway popup you really need a good quality decomp… I toss a husky 395 decomp into them… otherwise you can’t pull it enough to start them…. 😉👍

[@thedillestpickle]

MS391 has a decomp

[@dave5237]

Hello! Do you loctite those muffler bolts & I take it blue? Thanks!

[@bchase1980]

Does opening up the muffler void the factory warranty?

[@bryantitus6634]

These saws get a lot of hate, and while they are a big bore clamshell saw basically they aren't that bad. They really aren't as far off from a 036/361/362 as people try to make them sound like they are. They just FEEL clumsy and poorly balanced in my opinion. Feel cheap in comparison. But they do run pretty good. My brother has a 390 and I've run it a bit but I greatly prefer my echo 590 with the opened up outlet over his 390 in literally every way. When it's opened up like this it runs like a 64cc saw should. Not a screamer but just a good runner. Nice work.

[@tedneitzel]

I had one for a short amount of time but it's a heavy gutless boat ⚓!!

[@margihall6153]

Where’s that cute dog of yours? She’s the real reason I watch your videos…and to check your biceps out. 😉

[@zeromark202]

Wow what a difference, great video! What tach is that?

[@samishsawworks5870]

It's a tech-tach tt-20k. I went with it because it has one of the fastest refresh rates. You can run it wired or wireless. It does 2 & 4 stroke engines. www.amickssuperstore.com/DTI_2_Cycle_Two_Stroke_Hand_Held_Tachometer_p/dti%20tech-tach%20tt-20k%20tach.htm

[@ryanhubble9157]

How did you remove the limiters

[@samishsawworks5870]

This carb has the red plastic limiters. I use a screw (I grind the "point" off the tip of the screw) and thread it into the end of the red limiter until it's seated/grabs. There is a small "tab" that has to line up with the slot in the carb body. Then just use a pair of pliers and pull it straight out. Not my video, but this is how I do it. kzbin.info/www/bejne/aIKYYal3hLChi5I

[@ASSHOLE123456ish]

You want more RPM use a 20” bar an chain ! It does matter !

[@samishsawworks5870]

Hey, thanks for stopping in! I agree rpm matters. Not my saw though, so it left with the bar it had on it. Merry Christmas!

[@jeremymadej9227]

There goes the back Pressure In the engine.

[@im-that-guy-pal]

There is no point in making the exhaust larger than the intake port. You cant blow out more air flow than what is being sucked in. Matching port diameter is the best you can do for the exhaust unless the ports are inlarged. . It may sound better but its efficiency can only go downwards when you butcher the muffler like that.

[@iraagans3144]

Ah the ms391 ,a bloated 64cc plastic saw! Can you make it run better? Yup here's a 036!

[@ChuckBeefOG]

He probably put 87 octane gas in it. Edit: i see he did lol.