Need help with Stihl MS 361

[Wayne in La]

I have a fairly recent 361 that has begun to increase RPM and then die. It can be started by choking and setting trigger at high speed. I have installed a carb kit with no change in symptoms. I started with a carb kit because I have recently had a hole in the pickup line and thought some trash might have gotten by the filter.

Is this how an air leak sounds? If so what is more likely, a carb boot, cylinder base, or crank seals?

All suggestions are welcome.

Thanks,
Wayne

 

[Stihl051master]

Sounds like a possible air leak - one thing you can do (while the saw is running) if you suspect an air leak is to give a little shot of ether to the suspected area (s). If The rpms increase, you've found the spot where the air leak is.

You could also do a leak down test if you have access to the equipment.

 

[Trigger Man]

If he's got a lean running condition I would'nt be squirting ether on the saw to pin point the issue.

OP have you made any adjustments to the carb?
Check your impulse line?
check your tank vent?

 

[rxe]

Either air leak or fuel starvation. Find it quickly or it may eat your piston.

Hard starting sounds more like a fuel problem - or a catastrophic air leak, which would be obvious. Assuming you've got the carb back together properly (!), is the impulse hose in perfect order?

A pressure test would be needed to eliminate air leaks - ether is good in theory, but on something as small as a saw, it could get picked up some distance from where you spray it! Also getting at most of the places (crank seals, cylinder base etc) is pretty hard on a running saw...

 

[ECRUPPRECHT]

if he's got a lean running condition i would'nt be squirting ether on the saw to pin point the issue.

Op have you made any adjustments to the carb?
Check your impulse line?
Check your tank vent?

i agree...

 

[Wayne in La]

If he's got a lean running condition I would'nt be squirting ether on the saw to pin point the issue.

OP have you made any adjustments to the carb?
Check your impulse line?
check your tank vent?

I believe I was close on the carb adjustments. I have rebuilt a few carbs.

I am not sure how to check a tank vent. I am going to remove and replace the fuel cap to equalize the pressure and see if the symptoms go away momentarily.

The last thing I will do is start removing body parts until I can see the full routing of the impulse line.

Anything I should do differently?

Wayne

 

[Trigger Man]

That impulse hose comes off the jug and through the partion wall I think, I don't have my 361 anymore, so I'm not 100% on the routing.

 

[Erick]

Sounds like an impulse line????

Wayne, a pressure and vac test would be the best and fastest way to narrow down your problem. With that said I know not everybody has the tools just laying around to rig it up.

Start the saw and let it idle, while its idling take a screwdriver or your scrench and GENTLY pry the tank assembly away from the cylinder.
GENTLY.... your not trying to separate the parts here you're just trying to extend the intake boot a little so that if there is a hole in it it will suck more air and the idle speed will increase or if it's a bad leak the saw may just die altogether.

If there is no change try to spray a little carb cleaner around all of the possible leak points.... impulse hose, intake boot, cylinder base gasket, etc. The saw should die if you hit the leak. This all best done with the covers off so you can see what you’re doing and pinpoint the leak.

If all checks out here I'd look more at the carb.

 

[West Texas]

If it increases in rpm and then dies; that is a 'lean' condition. This is exactly how all chainsaws perform when they run out of fuel. So its a fuel related issue; you just start with the fuel filter for dirt, the fuel hose for air leaks, and if you have an extra carb on hand, swap the carb out, if no luck check the rubber manifold connection to the cylinder (found one that was loose today and partially off the cylinder), then the impulse hose.

A quick way to check for a seal leak is to start the saw and while its at idle, hold it horizontal, and turn it on each side. If the rpms change on either side versus sitting upright, then it could be a seal on that side.

Its either not getting enough fuel or its getting too much air. Trouble shooting it is a process of elimination.

 

[SawTroll]

I have a fairly recent 361 that has begun to increase RPM and then die. It can be started by choking and setting trigger at high speed. I have installed a carb kit with no change in symptoms. I started with a carb kit because I have recently had a hole in the pickup line and thought some trash might have gotten by the filter.

Is this how an air leak sounds? If so what is more likely, a carb boot, cylinder base, or crank seals?

All suggestions are welcome.

Thanks,
Wayne

Lots of good advice here already - here is my take on it;

Worst case it is an air leak, best case it is just a clogged tank vent or fuel filter.

I would have started with the simplest first = tank vent and fuel filter.

If opening the fuel cap helps when it is acting up, it is the tank vent.
Also try changing the fuel filter before you go any "deaper", they are cheap.

 

[AKDriveSprocket]

If the fuel filter has deteriorated some of the filter may still be in the line. If it is still in the line it gets sucked up the line and hits the screen in the carb.

 

[Wayne in La]

Seems to have been the tank vent. I was able to finish the job by opening the fuel cap periodically.
Can anyone give me the basics of clearing this model vent. Can it be disassembled? The only other one I have had to service was a MS 260 and it used a restricting screw in a piece of fuel line.

Thanks everyone for sharing your experience.

Wayne