041AV Suddenly loses power into cut

[NTXC8D]

Hey Guys,

Running a ( New to me ) mag 041AV with no issues for a little while now. Was bucking a tree the other day and saw was doing fine for about an hour. All of a sudden it lost all power about 5 sec into a cut (trunk) . Saw never shut off and didn't sound like it was running bad or anything. Was not bound up in cut either. Tried a few more times and the problem repeated itself exactly the same each time. Shut it down as to not damage it fearing lean condition.

Any known issues to look for while I'm pulling it apart? I'm guessing something rubber has cracked, like a line or diaphragm in carb? At first glance everything inside fuel tank looked normal.

Thanks in advance,
Jake

 

[lone wolf]

Hey Guys,

Running a ( New to me ) mag 041AV with no issues for a little while now. Was bucking a tree the other day and saw was doing fine for about an hour. All of a sudden it lost all power about 5 sec into a cut (trunk) . Saw never shut off and didn't sound like it was running bad or anything. Was not bound up in cut either. Tried a few more times and the problem repeated itself exactly the same each time. Shut it down as to not damage it fearing lean condition.

Any known issues to look for while I'm pulling it apart? I'm guessing something rubber has cracked, like a line or diaphragm in carb? At first glance everything inside fuel tank looked normal.

Thanks in advance,
Jake

Pull the muffler and look at the piston for scoring.

 

[NTXC8D]

Pull the muffler and look at the piston for scoring.

Went to go pull it " real quick" only to realize the port is under the carb so I'll have to tackle this tomorrow when I have more time to correctly execute. Thanks for the response.

 

[lone wolf]

Went to go pull it " real quick" only to realize the port is under the carb so I'll have to tackle this tomorrow when I have more time to correctly execute. Thanks for the response.

The intake port is under the carb, the exhaust is under the muffler. The exhaust side is the place where the most damage usually occurs. Also you could do a compression test.

 

[NTXC8D]

The intake port is under the carb, the exhaust is under the muffler. The exhaust side is the place where the most damage usually occurs. Also you could do a compression test.

The heat shield, under the carb is over the exhaust port so there's more to it than just pulling the muffler and looking. The exhaust port is directly above the intake port.

 

[lone wolf]

The heat shield, under the carb is over the exhaust port so there's more to it than just pulling the muffler and looking. The exhaust port is directly above the intake port.

So tomorrow then.

 

[NTXC8D]

Went to go pull it " real quick" only to realize the port is under the carb so I'll have to tackle this tomorrow when I have more time to correctly execute. Thanks for the response.

Sorry I realize my wording "under the carb" is misleading. Carb heat shield is in the way.

 

[cookies]

Muffler is a PTA to remove on those...I'd be looking at the impulse, fuel hose, pickup hose and fuel filter + carb guts, being that old they are known to need points/condenser replacements from time to time.

 

[djg james]

Hey Guys,

Running a ( New to me ) mag 041AV with no issues for a little while now. Was bucking a tree the other day and saw was doing fine for about an hour. All of a sudden it lost all power about 5 sec into a cut (trunk) . Saw never shut off and didn't sound like it was running bad or anything. Was not bound up in cut either. Tried a few more times and the problem repeated itself exactly the same each time. Shut it down as to not damage it fearing lean condition.

Any known issues to look for while I'm pulling it apart? I'm guessing something rubber has cracked, like a line or diaphragm in carb? At first glance everything inside fuel tank looked normal.

Thanks in advance,
Jake

Basically what @cookies said. I have the same problem with my 038 and have started a thread. The advice I was given was what he said. Also check the fuel tank vent. If it were me, I'd check the easy stuff first before pulling the muffler or the carb. My $0.02.

 

[stihltech]

Tank vent first. Very easy as it is in the cap. Clean it off good and see if you can suck air through it.

Yeah i know. Watch the fumes. After 40 years I don't even get a buzz.

 

[NTXC8D]

Pull the muffler and look at the piston for scoring.

Piston looks good from both ports. I don't know what is showing in 2nd pic on piston, but it is not actually there.

 

[lone wolf]

Piston looks good from both ports. I don't know what is showing in 2nd pic on piston, but it is not actually there.

As in the above post, said tank vent is next suspect.

 

[NTXC8D]

All the lines looked good and still flexible. Checking tank vent first as recommended, but if that is ok I'm figuring I'm going to have to get into the carb and might as well replace all the gaskets and diaphragms if I'm pulling it apart. Thanks for all of the input so far!

 

[stihltech]

Don't get the cart before the horse. Tank vent, fuel line (best to pressure test this one as many leak at the fitting in the tank).
Pulse hose cracks, intake gaskets suck in, cylinder gaskets leak, Get the easy stuff first. Many an 041 has been fixed on the fuel supply and intake sides.

 

[djg james]

All the lines looked good and still flexible. Checking tank vent first as recommended, but if that is ok I'm figuring I'm going to have to get into the carb and might as well replace all the gaskets and diaphragms if I'm pulling it apart. Thanks for all of the input so far!

Hope you have better luck with replacing the vent than I did. I put on a new one on my 038 and was hoping that would do the trick. Went to the log yard to test, but nope, have to keep pumping the throttle to keep it going. I'll keep on working on it.

 

[NTXC8D]

As in the above post, said tank vent is next suspect.

Checked the fuel cap vent and I couldn't pull/blow any air through it from either direction so, it is obviously clogged. Put some compressed air in from vent hole and shot out the white piece LOL! Thank goodness I found it. After cleaning the orifices out, the only way this cap will flow any reasonable amount of air ( by mouth ) when reassembled is with this set screw removed. If I put the set screw back in, it hardly flows at all. Any insight on it's purpose?

 

[djg james]

Checked the fuel cap vent and I couldn't pull/blow any air through it from either direction so, it is obviously clogged. Put some compressed air in from vent hole and shot out the white piece LOL! Thank goodness I found it. After cleaning the orifices out, the only way this cap will flow any reasonable amount of air ( by mouth ) when reassembled is with this set screw removed. If I put the set screw back in, it hardly flows at all. Any insight on it's purpose?

Not me, mine looks different.

 

[cookies]

Checked the fuel cap vent and I couldn't pull/blow any air through it from either direction so, it is obviously clogged. Put some compressed air in from vent hole and shot out the white piece LOL! Thank goodness I found it. After cleaning the orifices out, the only way this cap will flow any reasonable amount of air ( by mouth ) when reassembled is with this set screw removed. If I put the set screw back in, it hardly flows at all. Any insight on it's purpose?

It only allows a small amount of air flow, The carb diaphragm can overcome the vent hit it with a stainless brush to remove the crud then push it back in. Do not screw it in, only unscrew to remove. Did you remove the tank grommet and remove the fuel pickup hose? those pickup hoses get soft and collapse in use specially with a dirty fuel filter or if debris is present in the tank. Do not use compressed air on the carb, run it wih a in line spark tester to check for spark when it shuts off.

 

[Mike Ray]

mine does the same thing runs good when not in cut turned on side ,etc, put in cut may make one cut slows down and dies ,can choke it and will start ,but wont cut. replaced impulse line, fuel lines, filter , cked vent , going to rebuild the carb when I get to felling better (lung cancer), checked piston and cylinder look new. ps cleaned carb initially and made several cuts then went down hill.

 

[Snowman59]

I had a similar situation with my 041AV and discovered the fine mesh screen inside the carburetor was clogged. It would idle and run at slow RPM, but as soon as I would throttle up to start cutting, the engine would lose power.