MS361 Carb Help

[mb1973]

Hello folks
I have 361 that has faithfully cut all my firewood for about 12 years. The family and I moved into town and now heat with natural gas and the saw has sat unused for over a year. Started it up the other day and it runs as if the throttle is wide open. I tried adjusting the carb and the saw stays at WOT or stalls out. I changed out the carb with a rebilt one that I had sitting around and experianced the same issue. It does not seem to matter how I adjust the carb it goes from one extreme to the next. Any help would be appreciated. Just an fyi, the tabs on the carb are gone and the muffler is modified. Thanks.

 

[mkinslow]

I'd check for an airleak in the seals and such

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[buzz sawyer]

Maybe mice chewed a hole somewhere?

 

[Stihldoc]

The MS361 has one common problem that routinely occurs- the impulse hose comes off the back of the fuel tank housing, causing a huge air leak. Look between the cylinder and the tank for a curved black hose about 2.5" long. It connects to a nipple coming off the lower portion of the cylinder that is recessed in a piece of plastic shrouding. It then turns 9o degrees toward the clutch side of the saw, and then turns another 180 degrees toward the starter. After this 180 degree turn, it attaches to a small plastic nipple on the front (engine side) of the tank housing forward of the carburetor. It ALWAYS comes off the tank housing. If you find its come loose, be sure to replace the hose, not just reinstall it. Its not a special part, just a piece of Stihl R3 hose that any competent dealer will have tons of. The hose gets hard over the years and simply comes off the straight, non-barbed nipple on the tank. The other end of the hose is a little more challenging to remove- it is on a barbed metal nipple that is recessed in a plastic shroud (remember that I said that earlier?). The old hose tends to break off this nipple when you try to remove it, leaving about a 1/4" piece of hose that you have to remove before installing the new hose. No special tools are needed- just a bright light, a pick, and lots of patience.
The MS361's are getting old and seem to age very well EXCEPT for this one small issue. If the hose on your saw is properly attached, do a pressure and vacuum test to see if the crankcase has an air leak. There's no point guessing about what might be wrong- check the common, simple stuff and if that shows no problems go straight to a pressure test of the crankcase. Screwing around with this will waste your time and possibly cost you a cylinder & piston if there is an air leak.
This forum is full of knowledgeable people. What is often missing in their advice is that one needs a systematic approach to finding a problem. If you don't discover what the problem is, how do you expect to fix it?