Showing my ignorance (MS361 problems)

[Engineer]

In spite of all I learn here and on other forums and websites, I am pretty clueless when it comes to the guts of motors and engines.  Probably intentionally, as I am always afraid that I'll take them apart to fix, and either lose a critical part or fail to put it back together correctly.

However, it doesn't stop me from trying to figure out what is actually wrong, so at least I don't act the fool when the guy with the actual mechanical skill (i.e. not me) asks me what the problem is.

So - I was out cutting last night with my Stihl MS361.  It should be noted that the saw is currently running a 24" bar and a rather dull chain.  I was trying to cut a few cookies of various hardwoods off some very dry logs that have been sitting in the yard since at least spring.  I normally wouldn't have even bothered but the cookies are for a Scouting event where I will be teaching Cub Scouts about tree aging and growth patterns, and the parts of a tree's anatomy.  So I cut these cookies out of five different species - cherry, ash, Norway maple, butternut and black locust.  I expected the saw not to cut very well simply due to the conditions, but if I put any kind of pressure on it, or dug the dogs in to speed up the cut, I basically stopped the chain.  The saw sounds sick, and not in a good way.  I only run canned premix in it, it started up just fine and idles fine, it just seems to have no top end.  No significant power.  I also used to get what some of you guys call "four-stroking" after laying off the throttle, it would have this irregular engine burbling that settled down after a couple seconds.  It does not do that anymore.  This saw used to dig in and cut like mad and it won't do that now.  The saw is maybe 6-7 years old and has only cut 50-60 cords of wood.

What should I be looking at?  My first thought was the air filter - I cleaned it and it looks clean, but maybe it should be changed?  Any ideas? 

[thecfarm]

Gas filter? I've had some that will idle fine,but start to make them work and the saw can not get fuel and stops running. But will start right back up and idle fine.

[LeeB]

Admitting to ignorance on a subject is not showing ignorance. Trying to bluff your way through it would be. To be ignorant of something simply means you do not know. To chose to remain ignorant is another matter. I commend you for taking steps to banish your ignorance of the saw's problem. Having said all of that, I too am ignorant of the causes to your predicament. I'll follow along and see if we can both become a little more educated on the matter.
:D

[dougand3]

Does it rev up fine under no load? Dull cutters can stop a chain - I'd sharpen or get new chain.
If it bogs under no load, many possibilities. As above- fuel pickup clogged, hard or cracked fuel lines, carb out of tune, carb dirty or stiff diaphragms, muffler screen clogged, weak spark plug, etc, etc.

[North River Energy]

Go after the easy stuff, and if that doesn't work, check the end of the lever that opens the carb needle valve for wear/adjustment.

[beenthere]

Maybe the saw was victim to trying to jerk it out of a stuck cut, and damaged the connecting rubber between the carb and the cylinder... now it lets in air.

But... please put on a sharp chain. ;)

[sablatnic]

Screen in the exhaust clogged?

[Gearbox]

Have you adjusted the high speed jet . Hold it wide open no load turn the HS screw in till it screams and back it out till it blubbers a bit { 4 stroking} then sharpen it and try it . I have a 361 and it will cut almost up with my 044 . Gearbox

[WDH]

Pull out that muffler screen and throw it away. 

[nitehawk55]

If it's loosing power or running poorly it may be as simple as the spark plug misfiring some . Plugged muffler screen or air filter could do it to but from the way you're describing it sounds like it's running rich and low on RPM's . Are you noticing a lot of smoke from the exhaust or fumes ?

[Engineer]

I'm gone for the next couple of days but I'll be tearing into this on Sunday to try some of you guys' suggestions. I'm guessing it's a combination of things. It's never had a new plug so I'm going to check that and the fuel filter first. It does run at WOT no load but seems to not be reaching peak RPM.

[HolmenTree]

I hate offering diagnosis advice over the Internet not having the saw in my hands.
But I'll throw a few out there. Your saw is approximately 6 years old which may have build up of debris in the cylinder cooling fins causing overheating. Also you mentioned spark plug was never changed?
Carb diaphragms may be stiff and need changing......spark arrestor screen plugged?

[SineWave]

Screen in the exhaust clogged?

+1. You can pull the screen off with a screwdriver, and then heat it with a propane torch to burn off the carbon.

Also, I opened up the muffler in my 361 and got a saw tech to richen it up the right way (if you open up the muffler, don't neglect to richen it up or you could burn up the saw due to a lean condition) and it probably pulls 20% harder now.

[49er]

  First thing I do to a saw I am unfamiliar with is a compression check.
Next is pore out the gas and inspect the fuel line and filter, all the way to the carb. Observe the condition of the fuel. Check impulse hose too. Put a driver on every screw and check for tightness. I do this before I even try to start the saw. Also, take the plastic off and blow out all the dirt and crude. A large percentage of the time you don't need fancy trouble shooting abilities, just be observant.
  Most of the time, if a chainsaw won't run right it will be fuel and not ignition.
After a while you will learn by the nature of the symptoms what the problem might be. I think everyone who works on things will run into some problem that just gives them fits that make ya want to pull your hair out.
  The more information you can give the more likely you will get the correct information for solving the problem.

[Kingmt]

My 038 stopped running 2 years ago so I ordered a new fuel filter & gas line. The filter was perfect but it did need the new line. After putting it back together it'd still cut out on high end & didn't have the power to cut. I didn't need it so it sat till about a month ago when I decided to look at it again. I seen the line on the back of the carb was bad going to the block (not the manifold). After replacing it it was running better & would cut but still had a hiccup at WOT so I took the carb apart & cleaned the chips point from under the advance pump. Everything else looked new in the carb but after putting it back together it seemed as I took a step backwards. I backed the high speed screw out until it seemed to be running right which was 2 whole turns. The saw cuts great now but it still has a cutout at WOT but held just under WOT I never hear it. I had already done the other checks mentioned above(expect compression) with nothing found.

I'm still trying to figure out what is going on with mine. No used why I have to be 2 whole turns out of why I have to keep it just under WOT.

Good luck on finding out what is going on with yours.

[Texas-Jim]

Ethanol is a killer on fuel lines. They crack and get brittle and let air suck in. Plus its easy to check.