041AV Suddenly loses power into cut

[djg james]

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.

Something for me to look at too.

 

[NTXC8D]

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.

Will check fuel pick-up hose and filter tonight. I did notice the tank grommet was slightly loose, but figured that would only cause a fuel leak and not a performance issue. I'm not sure what you mean by don't screw it in? Only way I can put the set screw back in its original location would be to screw it in. Or are you talking about pushing the white orifice piece back into the cap?

Spark is good, it never shuts off unless switched off.

Hopefully I'll have it back together tomorrow and can test it out.

Thanks

 

[HarleyT]

It is hard to determine if you have an ignition problem, you should go ahead and clean and adjust the points.
Also, the older saws had a rebuildable fuel filter. After 20-30 years or so, the foam insert can break apart, and that is what you will see in that screen in the carb, but you should completely rebuild the carb, make sure that the stuff has not partially clogged the passage under the needle, and other orifices.

Partial clogging can let the saw idle/run fine, but run lean when the saw is put under a load.
Also, the fuel line can get real soft and collapse/suck together when turned on it's side or in high rpms.
Of course there is a stack of crap under the carb, and lots of gaskets, and if things were loose, go back with a drop of blue loctite.

 

[HarleyT]

Will check fuel pick-up hose and filter tonight. I did notice the tank grommet was slightly loose, but figured that would only cause a fuel leak and not a performance issue. I'm not sure what you mean by don't screw it in? Only way I can put the set screw back in its original location would be to screw it in. Or are you talking about pushing the white orifice piece back into the cap?

Spark is good, it never shuts off unless switched off.

Hopefully I'll have it back together tomorrow and can test it out.

Thanks

If you are putting on a new vent hose, do not screw in the little setscrews, but push them in. Screwing them in can cut threads into the hose, and not let air pass.

 

[pioneerguy600]

The aftermarket fuel filters will breakdown in less than a year iif the fuel has ethanol in it, cheap crap is not intended to be subjected to ethanol.

 

[thenne1713]

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

SOMETIMES,,, I have read, a SUDDEN POWER LOSS, is actually a bar-tip sprocket that is SEIZING when hot? Engine off, immediately check chain rotation?

 

[kd.rodgers]

Since you said it sounded fine otherwise and wasn't sputtering/dying, a sudden lean condition from a cracked line or diaphragm would be my first hunch too. The fuel lines and impulse line are common failure points on older saws, as well as those pesky carb gaskets and diaphragms, unfortunately.

Clean out the carb while you have it opened up, replace any cracked lines, and make sure the impulse line didn't get pinched/disconnected at some point as well. Sometimes they can get bumped loose surprisingly easy.

 

[HarleyT]

The aftermarket fuel filters will breakdown in less than a year iif the fuel has ethanol in it, cheap crap is not intended to be subjected to ethanol.

I have been soaking in ethanol for a real long time...

 

[Kenskip1]

How about putting in a new spark plug?

 

[pioneerguy600]

I have been soaking in ethanol for a real long time...

That is why you are the 041 specialist.

 

[stihltech]

The 041 is pre vent hoses. The vent is a screw insert in the cap. They do screw in lightly. Does not take a lot to plug them, especially after 40+ years.
The fuels hose and fitting is an issue because it causes the system to suck air and not fuel. The hose swells and loses it's seal. It is also a quite long hose in comparison.
This is where a pressure tester comes in handy. Plug off one end and pressurize. A little soap and water will tell the tale. Also watch how far the hose in the tank blows up. It should not.
The screen in the carburetor is a good indication of hose and filter degradation.

 

[Okie]

A tool I keep handy to make sure that a chainsaw is not running lean in a cut and overheating is a IR thermometer. I use a 3M but others are available at a very reasonable price.

If a chainsaw starts acting up like bogging or slowing down in the cut the engine can ruin itself really fast due to piston expanding into the cylinder wall. When using the IR just aim it at the block and if the block temp is getting to 350F it's getting too hot.
Just play with the IR thermometer on a good normal chainsaw first to get the idea.

You say your piston still looks ok so you are probably not overheating, but the IR thermometer lets you know such without guessing if it's lean or heat related.
The IR thermometer is also handy for other purposes for a instant heat read, just to mention one is for example comparing cylinder temps on multi cylinder engines, AC temps,.

 

[NTXC8D]

A tool I keep handy to make sure that a chainsaw is not running lean in a cut and overheating is a IR thermometer. I use a 3M but others are available at a very reasonable price.

If a chainsaw starts acting up like bogging or slowing down in the cut the engine can ruin itself really fast due to piston expanding into the cylinder wall. When using the IR just aim it at the block and if the block temp is getting to 350F it's getting too hot.
Just play with the IR thermometer on a good normal chainsaw first to get the idea.

You say your piston still looks ok so you are probably not overheating, but the IR thermometer lets you know such without guessing if it's lean or heat related.
The IR thermometer is also handy for other purposes for a instant heat read, just to mention one is for example comparing cylinder temps on multi cylinder engines, AC temps,.

I have an IR gun, I'll check the block when I run it again.

Looking to get it all back together today .