Stihl 041 AV not supplying fuel to the carburetor

[Swiss]

I have an older Stihl 041 AV saw that would not start. To troubleshoot the fuel supply, I poured some gas mix directly into the carburetor - it fired up immediately, but stalls when that fuel is burned. I removed and checked the fuel lines, and they are clear. I filled the tank with fresh mix. Still no luck. Could someone briefly explain how the fuel is supplied to the carburetor, and recommend some steps to troubleshoot the fuel supply problem?

 

[Lakeside53]

The gas is "pumped" from the tank by impulse pressure changes of the crankcase being applied to the crab pump diaphragm. The impulse line connects to the carb end cover plate. The fuel hose connects to the side elbow.

Generally, if the saw has been stored for a while the carb is gummed up. Pull the carb, clean out the gunk with White spirit (Coleman stove fluid) and put a new kit in it. Obviously check the integrity of the impulse and fuel lines, and put in a new fuel filter. It might be that you have an air leak from a crank seal, but most likely you just need to fix the carb.

An easy was to check the fuel flow to the carb is just connect another fuel source (like a weedeater tank) to the side elbow, and gravity feed it. If the saw runs fine, the problem is impulse; if not, fix the carb.

Make sure your H+L screws are adjusted to "standard" settings before getting too deep into the problem. I'd start with 1 1/8 turns out from seated.

 

[Dan Forsh]

I have one with exactly the same problem. I have a few days off this week, so I'm going to work on mine. We can compare notes as we go.

I actually have another one I bought for parts for this one which runs okay, but bogs down and stalls in the cut.

 

[Fish]

The 041s are well known for air leaks in the stack of blocks, plates and gaskets between the carb and engine, as things rattle loose, and gaskets come apart. It may have been tightened by someone in the past that did not check the gaskets,
check this when you go through the carb, and that should help in your problem.

 

[cunrya]

Change the fual filter first of all, before you go tearing into the carb ect. True a carb overhaul wouldn't hurt a thing, but sounds to me like it might just be that the filter is broken down or clogged. Pull the filter out (remove the top cover and pull it out through the top of the tank) inspect its condition. If appears to be crumbly and desintigrates when handled, you need to tear into the carb and blow out the internal orrifaces and screens, put a rebuild kit in while your at it for good measure (filter and carb kit shouldn't be more than $25. If the filter appears ok, replace it and see if the saw runs. I'd replace the fuel lines while you were at it since there only a couple bucks and you have it torn down already, will clear up any air leak issues.

 

[Dan Forsh]

Well I think I've got mine done. Pulled the carb, dismantled and cleaned it. The metering diaphragm looked a little tired so I changed it for another used one, but in better shape.

Put it back together it eventually started and ran okay. Then decided to vibrate itself apart and stopped. Like Fish says, make sure everything is tight, mine lost two casing bolts and loosened the carb nuts about a quarter inch. I took it apart again, put everything back where it should be and tried again. Took about 15 mins that time and finally started with a little fuel down the carb. Has started okay since (touch wood).

I'm gonna put the bar and chain on tomorrow and see how it is in the cut.

 

[Swiss]

Thank You Very Much

Thanks to lakeside53 for the excellent description of operation, and thanks to FISH, Cunrya, and Dan for the excellent troubleshooting advice. I will go after it tomorrow by trying the alternate fuel supply technique to determine if the problem is the carburetor or fuel supply to the carburetor - and then proceed from there.
Congratulations on your success Dan!