044 drops spark when hot

[Hack]

Howdy, longtime lurker here. Many thanks for the content you've shared, this site is great.

Saw history...I loaned my slant-fin 12mm 044 to a coworker and he returned it with a burned pto-side bearing. Lesson learned. I got enamored with someone's 046bb / 044 build, so I bought a baileys 046 big bore cylinder, smoothed and enlarged as best I could with a straight die grinder, and installed, along with new bearings and seals and such. Tried to match port timing of the OEM 044 cylinder, but that's a pretty distant memory. Saw seems to pull hard but is a bit peaky and goes thru gas pretty good...works fine for me cutting firewood. Have since read on here that the 046bb kits are a bit pinched, so may be seeking an OEM 046 cylinder for it down the road, but that's another matter.

I ran it this way for probably 5 or 6 years. I don't cut a lot, just enough to heat my house and help my dad and inlaws with theirs.

About a year ago, it developed a condition where when run hard, it will drop spark a few times then die. It's not the gradual fall-off with running out of fuel, rather it's very sudden. If I rest it in the breeze for a few minutes, it will light right off and run until it gets hot again.

Throwing parts at it, I replaced impulse and fuel line with OEM stihl. I tried an aftermarket coil. I checked fuel tank venting. No smoking guns.

Ideas: do the flywheel magnets weaken, and perhaps get temperature-sensitive? Can a fuel line or impulse line collapse with temperature, even if OEM?

Grateful for any ideas and direction you might have.

 

[dall]

seen on a couple 046 the flywheel would go bad
so id think other models would as well

 

[drf256]

Magnets can go bad, but it’s generally an all or none kinda thing. They lose polarity more than magnetism itself. A good hit to them can make both magnets the same polarity which will cause the coil to not generate spark.

What you’re describing is a classic electrical issue. Goes away when the saw cools. Could still be a fuel issue, but usually the tune will get wonky before the saw stops running. I’ve seen oem fuel lines soften and suck themselves over the years.

Dumb question, but did you replace the spark plug? I put $200 into a Honda 4 stroke one time and it was the $2 plug that was the issue.

I‘d replace the coil and plug lead with a used oem one. Easy to find, the same coil 024-044. Used the “dummy” coil which has no spark low rpm retard feature. On ebay, people sell the same coil for an 044 for much more money than the same 026 coil. The coil is the same but the spark lead is a bit shorter on the 026.

 

[Stump Shot]

While not as likely, don't forget the shorting lead in the list of electrical debacles. Simply disconnect and run to confirm.
A cracked spark plug though would surely fit the failure description.
I even had one saw act like this and it was a bad ground to the coil, so keep checking everything until it's found.
The inline neon spark tester helps in confirming this by visual means while running the engine in real time, inexpensive and handy to have around.

 

[Stump Shot]

While I might save it for last, I wouldn't rule out a bad flywheel. I've seen some that would only generate a weak spark and would start then die, however it wasn't this particular model or even brand of saw. Never know though, stranger things have happened.
Good luck in your diagnostics @Hack

 

[Wonkydonkey]

I would go with what drf256 says, it’s the spark plug.

I had a friend with 056. It would run all day but switch it off when hot it would not start till cold, rinse & repeat…..

I was there on a particular day and said let’s swap spark plugs, and both saws were hot . I bet you can guess what happened…

Mine didn’t start and his did.. so I said fug your spark plug you can have it back, he just laughed and said my saw works now

It’s a cheap way to test the spark plug, but it’s not always the only cause of the problem..it could be the coil as well but that’s the next step

 

[Al Smith]

Might sound nuts but I have an Echo weedwacker one of the flywheel magnets goes weak over the winter when it's not in use .I renew it by stroking it with a rare earth magnet .I haven't tried it in 6-7 years because I think I have 5 or 6 that will start .Those were all freebies except one Stihl which I bought new about 8 years ago ."New " for me is a very rare thing I do .

 

[Hack]

Update: bought an OEM 026 coil and plug wire on ebay. Plug wire is a touch shorter but still able to weasel onto the plug. Started and ran very nicely, carried power through about 4 maple cookies 16" or so, then dropped spark again. I think that rules out the coil. Slightly different behavior though; it seemed like it was slower to get to the spark-drop point, and it got back to full spark sooner after a shorter cooling period.

Ran it with the fuel cap tightened over a toothpick for positive venting, no change, so that rules out the tank vent.

Think I'll get a new/used flywheel on ebay next.

Forgot to mention that it has a new plug...bosch or NGK can't remember. I replaced that as part of prior diagnosis attempts.

 

[Maintenance Chief]

Pull the muffler.

 

[drf256]

I’d replace the plug, again. It’s cheap and easy.

Is the flywheel key sheared? I’d check that as well.

Disconnect the coil wire (the one that plugs in) and run saw. You’ll have to choke to kill it, but you can rule out something where those wires are somehow grounding out with heat.

Check your compression. You need fuel/spark/compression for a saw to run. The spark has to be at the right time. Could be that the AM jug is going out of round with heat-I know it’s a long shot, but check it out as well as the piston skirt through the exhaust port.

Try another carb if you have one as well. Too bad you’re in Canada. Many of us have used 044 parts, but shipping to you is quite expensive and also a PITA because of the custom forms.

 

[Maintenance Chief]

I am rebuilding a early flat top 066 that was doing this, the vinyl bearing spacer was coming apart.
Glad I didn't keep running it!

 

[Hack]

In the process of diagnosing this earlier this year, I've had the covers off and the cylinder off. I noted no unusual wear. Good compression, takes a strong drop to pull, hot or cold.

I'll try the coil wire unplug trick, and another plug replacement. I can't wrap my mind around the flywheel key shearing...it runs well and strong when it's cold-to-warm and I can't associate that with a poorly-indexed or slippin flywheel.

The little profile flag indicates Canada but I'm in NW Washington up near the border. Lots of family and recreating up there though, so I'm fluent with multiple Canadian dialects: north/central Alberta (nearly every spoken sentence ends inflected as a question) and upper Vancouver Island (odd/hard emphasis on some syllables...an-CHO-vy, HAAAL-ies (halibut)).

I haven't done anything with the carb, dating back over the 20 or so years I've owned it. New OEM impulse and fuel per first message but nothing else fuel-wise.