Stihl MS 361

[WCarp]

I tried adjusting the high speed carb jet on a Stihl MS361 with a small flat blade screwdriver but it just turns around and around without doing anything. I tried to look down the tiny hole/tube for the high speed adjustment and couldn't really see what was down there. It didn't seem to be plugged. What kind of screwdriver does it take to adjust the carb?

Thanks

[sawguy21]

Welcome! The carb is adjusted at the factory and is supposed to be left alone thanks to th EPA. There is a special tool that can be used to make minor adjustments but we are not supposed to have it. Others more familiar with that carb can tell you which style is needed.

[John Mc]

If you search for "chainsaw carburetor adjusting tool" on eBay, you'll find several sellers with sets of three different types of screwdrivers for adjusting carbs. They only run about $8 (generally, these kits include the Double D, Pac Man, and Splined type screwdrivers). There are also people selling 8-piece kits with a couple more variations of tools. I'm not sure what type of tool your MS361 uses, but one of those types should fit, and someone here will know which type you are looking for.

Once you have those, you'll need to figure out how to defeat the carb limiter on the adjustment screws. It's been too long since I've looked at a 361 to remember what Stihl's method is. On my Husqvarna/Jonsered saws, it was just a plastic cap with a little tab sticking off, preventing it from being turned beyond a very narrow range. The intent is that the dealer removes the cap, makes an adjustment, and replaces it. I just shaved the tabs off of mine with a sharp knife. I do not recommend just permanently removing the limiter caps: some saws rely on the bit of friction the caps add to prevent the screws from turning on their own due to the vibration of the engine.

I know I read somewhere about someone using an old wood screw or deck screw to screw into some styles of plastic limiter caps as a tool to remove them. I've never done that, but perhaps someone here can comment on how that works.

[lxskllr]

My 362 had caps, and they were so deep, I couldn't see how it went together. I never got around to checking it out before I lost the saw. You probably need to remove some top plastic to get a good view of the situation. There should be a little adjustment with a flathead screwdriver. It'll be hard to find the slot, but it should be there.

[Mad Professor]

Take the AF cover off and clean out all the crap inside, then clean the air filter real well.  You don't want to try to adjust carb with dirty AF.

You will see plastic caps on the Hi/Lo adjustment screws, that limit adjustment range.  If you can't tune within the limits, you need to remove the limiter caps to adjust the screws.  The caps need to go back on or the screws can "drift", loosing the tune and maybe hurting the saw (lean condition).

Lots of variations on the caps, how to remove them, how to put them back on, depending on particular brand/saw/year/carb.

Try doing a search specific to MS361.  It would be good to have carb brand/model handy too.

Edit: A little research, limiter cap stihl part # 4203 121 2700

Some dealers won't sell you these as an "EPA" item

See if you can get new ones before you remove/damage/cut the old ones
 

[Gearbox]

Mad Professer I have been around saws all my life and if a limiter cap comes off it stays off . I have never had a saw adjustment drift as you put it my 361 runs from below zero to 80 degrees above . A guarter turn one way or the other is all it needs spring and fall . WCarp If you are not skilled at adjusting a saw spent 20 dollars on Amazon for a chain saw tach or just have a dealer adjust it . It would be a shame to melt down a healthy saw because you got it to lean . Ask me how I know about this thing is running good today for 3 cuts poof melt down .

[Mad Professor]

Mad Professer I have been around saws all my life and if a limiter cap comes off it stays off . I have never had a saw adjustment drift as you put it my 361 runs from below zero to 80 degrees above . A guarter turn one way or the other is all it needs spring and fall . WCarp If you are not skilled at adjusting a saw spent 20 dollars on Amazon for a chain saw tach or just have a dealer adjust it . It would be a shame to melt down a healthy saw because you got it to lean . Ask me how I know about this thing is running good today for 3 cuts poof melt down .

Gearbox,
I too have been running saws since the 1970s and fixing/rebuilding my own.  The pre-EPA saws had springs on the Hi/Lo carb screws to keep the adjustment in place.  The limiter caps do this on the newer carbs.  You have been lucky yours have not lost tune on the lean side of things, yet.  All that is keeping yours in place is an o-ring.  If it gets worn, the screw will move.
Why loose a saw for saving $1 on a new limiter cap?
I've never used a tach to tune my saws.  With a clean air filter and sharp chain. I set them rich out of the cut (4-stroking sound), then put them in a full cut.  If they are still rich in the cut (4-stroking), I adjust ~1/8 turn on the Hi screw at a time.  Check out of the cut, then back in the cut.
Sometimes it's worthwhile to go back and check Lo/idle, then Hi again.  For Lo I find where it dies from too rich, and races from too lean, then set 1/2 way between.  If the bogs coming off idle it's still a bit lean and Lo gets a little turn out.  If it loads up idling it's a bit too rich.  If Lo is way off I might have to adjust idle too.
MP

[John Mc]

Tuning by ear can be very accurate, once you develop the ear for it. Check out Madsen's Saw tuning & repair page click on the "Saw Tuning" link and they will walk you through it. The link includes some audio files so you can hear what to listen for (you will need good speakers or good headphones. Most laptop speakers are too poor quality to really hear what is going on.)

[lxskllr]

I'm not that good at tuning by ear, but I start very rich, then back off the screw over several sessions cutting wood. The low screw is a bit of a mystery to me. My new PoulanPro was giving me problems at idle, and I /think/ I fixed it by turning the low screw out a fair amount. I think it was 1.25 turns. Still need to spend more time with it, but I think it's fixed.

[WCarp]

I found out that the problem was that the screwdriver was a little too wide at 3/16" to go all the way in the hole. A 1/8" screwdriver worked okay but I had to push hard to get it in all the way. The the max rich RPM was 14,200, which is a bit high, so it looks like I have have to remove the limiter cap.

[ZeroJunk]

If the saw has the little red caps you can just screw a drywall screw in, line up the tab and snatch it out. Turn the needle maybe a quarter turn richer and push it back in.

I suspect of all the people who think they can tune correctly by ear maybe half of them can.

You can do timed cuts if you are really bored.

They will do a pretty good job at a wide RPM range which is why so many think they are an expert tuner.

[Gearbox]

I just checked 2 saws for my nephew both 72 cc for 2 pro loggers . one was at 12,300 other was at 12,400 .The one at 12,4 sounded wrong so we checked .Both saws tuned by ear . limiters still in place .

[ChrisRoss]

Unless you are sure what you are going to do, I suggest to stay from the carb adjustment. You can do minor adjustment, but still, if this is your first time, I suggest you take help from a technician.