MS 362 Tune Up Questions

[dpeterson3]

I'm trying to get a MS 362 running right for a friend. I've worked on a lot of 2 stroke air cooled motorcycle engines before, and thought a chainsaw engine couldn't be much different. I guess I was a bit wrong. Anyway, it will start, but it wouldn't idle or run. I pulled the plug, and there was a lot of gas in the cylinder and some carbon buildup on the piston. The plug was black as well. No problem I thought, Its just running a bit rich and needs to be leaned out some. This is where I get a little lost. I'm use to carbs with 1 air screw. As I understand it. There's 2, and an idle speed screw. The L screw adjusts the fuel/air on the low end and the H screw adjusts the mixture on the high end. I set the low one back to factory and played with it until the saw idled a little too well (chain didn't stop. Need to readjust). Thats about 2 and a half turns out. I can't get it to run correctly when cutting. Here are my main questions:

1) I run the H air screw all the way in. Factory is 3/4 turn out. It will only come out 1 turn, and then it stops. It won't go further. Is this correct, or do I need to tear the carb apart?

2) Is there some other trick to getting Stihl's to run right on the high end? I've seen people mention checking the exhaust for carbon buildup. Anything else I should look at?

[beenthere]

Welcome to the Forestry Forum.
There are several very qualified techs and knowledgeable members here that can help. Plus there are several threads that have discussed adjusting the carb.
Maybe a carb kit is required. 

[Andyshine77]

The 362 has a limiter that prevent the the H speed jet from moving more than a half turn or so. Normally you want the H backed all the way out against the stop, but even then that's normally a little too lean for my taste, but the saw should still run and cut fine. What you may have is a plugged spark arrestor screen, remove it from the exhaust muffler and have a look. My guess it's plugged up with all that carbon pretty good. You can simply leave the screen out, or heat it up red hot with a torch, that will burn off the deposits. 

The high idle isn't a problem. As long as the acceleration has no hesitation the L is set properly, if the chain is spinning simply turn out the LA screw.   

Here is a video I made for people that aren't familiar with tuning a saw.

www.youtube.com/watch?v=Qjb9_UIgSdY&list=UUDzYN6LbndM64YHQp_JOb4Q     

[John Mc]

Most modern saws have limiters installed on the carb mixture screws (an EPA requirement to prevent someone from adjusting it too far out of whack, and increasing emissions).  Generally these are set up to run on the lean side (sometimes too lean) to help the saw pass the EPA emissions check.

If you are running too rich, you have to wonder what happened to change things.  If the owner, or someone else didn't adjust it too rich, then you have a problem to solve.  I'd start with cleaning the air filter, and checking to see if the spark arrestor screen on the muffler is plugged. Both of these can make a saw run too rich.

The L screw is for adjusting the mix at idle, the H screw at WOT (wide open throttle). Generally, these are the only two settings where you should run a chainsaw. If the saw is not under load (i.e. cutting wood), you should only run at WOT for brief periods.
Check out Madsen's web pages for info on tuning/maintenance tips

[JohnG28]

Like Andy said, it sounds like you have it close on the L and just need to adjust the LA (idle) screw to get the chain to stop. And if the plug was fouled then likely the same in the exhaust screen.

[dpeterson3]

Been almost a month. It took me until today to get time to look at that saw, though. Spark arrestor was nice and clean. I think I solved it, though. It has a spark problem before that turned out to be that spring they put in the plug wire made itself a hole and wasn't making contact. Anyway, when troubleshooting that, we removed the coil pack to check it. I hadn't gapped it properly when it went back in. Redid the gap on that, and seems to run just fine now. I'll probably have to readjust the air screws again, but I think that solved my issue. Now on to repair the 036 we found buried in the shed. 

[dpeterson3]

Spoke too soon. They took it out and tried it this morning. They told me it ran fine and cut great until it warmed up. Once it was warm, it was bogging down. I suspect its getting too much fuel. That's what it was doing the last time it did this. I'm not sure what that's a sign of. If it was a motorcycle, I would turn the air screw out some, but not on this saw. Suggestions?

[Andyshine77]

Spoke too soon. They took it out and tried it this morning. They told me it ran fine and cut great until it warmed up. Once it was warm, it was bogging down. I suspect its getting too much fuel. That's what it was doing the last time it did this. I'm not sure what that's a sign of. If it was a motorcycle, I would turn the air screw out some, but not on this saw. Suggestions?

If it was getting too much fuel it would run better when warm, not worse. In fact if the engine isn't getting enough fuel, it will overheat and lose power. At this point is seems like you'd be better off taking the saw to a reputable dealer and have then look the saw over, as the saw could have other issues than simply the carb being out of tune.

BTW make sure you're running fresh fuel mix. 

[dpeterson3]

I got to look at it again today. I took the plug out and I guess regapping really helped. When they ran it last, it was running lean instead of rich like it had been. Plug was much whiter than it should be and there was no gas smell in the cylinder. I don't see any cracks in the fuel line, but I'll replace it anyway. It left some residue on the carb intake line, so I think its starting to go. While I have it apart, I'm also going to rebuild the carb. Thankfully, the cylinder wall and piston don't show scoring or cracking, so it didn't get too hot. I don't see any signs of an air leak on the intake, but should I try to replace it anyway? Also, anything else I should look at while I've got it apart? This is all for a non-profit, so the budget is kind of tight. That's why I'm doing this instead of a professional.

[sablatnic]

The problem could be the filter INSIDE the carburettor.  Have had that happen to me.

[SliverPicker]

I have a 362 and have run the snot out of it.  It is so finicky that I have to adjust the carb just going from shade to sun.  This isn't what's wrong yours, but it ain't helpin'!

PS Great saw.  It has grown on me.  I'd buy another.