saw stutters and lost power

[sven556]

I have been rebuilding a stihl 041 av and finally put it into some wood today. I ran it in some old 12" cottonwood for half a dozen cuts, nothing to really stress it! Then, I went back to work cutting some osage orange fence posts. So, this was all small hardwood, only up to about 8 inches. after about 5- 10 minutes of that the saw started to stutter, lost power, and popped a few times (almost like a backfire?). Any ideas what could be the issue?

A little background here. I am new to adjusting carbs. I hadn't got the idle of the saw set just right, but I think the high side was set good. have a tachometer coming in the mail, but after I ordered it I realized I'm not sure how to use it on a saw. It uses reflective tape to detect the rotation. Should I put the tape on the clutch, without a bar and chain?

 

[cus_deluxe]

Id be checkin for spark on that old pig first. Have u tried restarting it?

 

[sven556]

It does have an SEM ignition module. It seems to start decent. Usually a few pulls even after it starts sputtering.

I have been wondering if the timing is off, but if it runs good for the first 10 minutes, than could it be the timing?

 

[Efisher26]

I'd say carb kit, check gas line/filter. Timing would make it never run right I'd think


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Just a home owner that likes the older better made machines

Craftsman 3.7 x2
Husqvarna 36

 

[sven556]

I put in a new carb kit and fuel line/filter. I'll check them again though, just to be sure. How would the carb/gas line/filter act up after 5-10 minutes?

 

[Efisher26]

Is the carb adjusted while eng is hot?


-•------------------------------------------------------------


Just a home owner that likes the older better made machines

Craftsman 3.7 x2
Husqvarna 36

 

[pioneerguy600]

More likely the old coil heating up and when they do the spark goes way down. Most often once the coil cools off it will produce spark again. The saws like the 041 with the coil under the flywheel are very prone to overheating, the heavier the load on the saw the more heat trapped under the flywheel.

 

[sven556]

How would I check if the coil is opening up when hot?

 

[pioneerguy600]

Only good way to check is to pull the plug immediately, reattach the high tension wire,ground the plug against the cylinder and pull the saw over, watch for spark across the electrode. You have to be quick as when the coil cools some it will spark again. The coil will eventually die or the timing will go way off, the saw won`t start at all when the coil gets bad enough.

 

[Full Chisel]

Yep, sounds like a faulty coil to me as well. Maybe just a fouled plug if your lucky.

 

[sven556]

I tried the saw again today. If the saw dies I am able to restart it again. After it died I tried a spark plug that I opened the gap on and I couldn't see the spark (this was in bright sunlight) but I could hear it snapping. I did notice that when the saw starts bogging down like it is going to die, if I let off the throttle and let it go to idle, the saw won't die and I can keep it running doing that. I'm wondering if the timing is getting thrown off once the saw heats up or maybe I didn't have the saw warmed up all the way when I adjusted the carb? I think I'll go try to adjust the carb again once the saw is warmed up and sputtering.

 

[alexcagle]

Check the screen inside the carburetor.

A backfire out of the carb can be from an overly lean condition.
A backfire out of the exhaust is usually ignition related.
Could be either a bad plug as Full Chisel said, a sheared flywheel key that only moved a little, or it's the sem ignition.

A cheap diode spark tester is what you need. They can be used while the saw is running, and you can see the ignition quit sparking as the saw is at full speed.

Make sure the impulse hose line is clear, and it's not blocked. It should flutter as the piston goes up and down. I had an 041 once that had set for a few years, and the port inside the crankcase had goo in it from a bar oil leak that solidified.

 

[Efisher26]

I bought a inline spark tester from harbor freight, works good, can see spark In sunny conditions


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[giver]

Unplug your kill switch and try it sometimes when they get old they will make contact with the vibration and you will lose your spark

 

[hotshot]

A cheap diode spark tester is what you need. They can be used while the saw is running, and you can see the ignition quit sparking as the saw is at full speed.

OK Alex, great advice, but you've got me on this one.

WTF is a "diode" spark tester? I've only seen an inductive w/ bulb, a gap, or an inline filament bulb type spark tester.

Maybe you're thinking of a noid light for fuel injector control signal testing?

 

[Efisher26]

LED "light emitting diode"?


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[alexcagle]

Yes, an LED.
An incandescent works too though.
What's key is that you test it with the plug installed. The impedance load is higher under compression.

 

[hotshot]

Yes, an LED.
An incandescent works too though.
What's key is that you test it with the plug installed. The impedance load is higher under compression.

Filament bulb is incandescent...mine don't last long.

Please post up a manufacturer & model number of tbe LED type (is the Stihl ZAT4 using a LED???) when you get a chance!

 

[sven556]

Messed around with the carb settings yesterday and now the sputtering and loss of speed/power seems to have gone away. I think I have everything set pretty well now. I haven't put it in wood yet so I'll see how that goes. Got the idle set so the chain doesn't spin, but there is just a bit of hesitation when the throttle is pulled. I think the high is set fairly rich but I figured I can check the speed whenever I get my tachometer and adjust from there.

Thanks for all the help!

 

[TPA]

I used fuel line on the impulse line once. It turns out that when it gets hot, it collapses, then reforms properly when cool fuel runs through it, so that it looks like an intermittent problem. It took a while for me to find that one. Maybe check to see what type of hose you are using for the impulse line.