Stihl 029 chainsaw dies when warm.

[ChaneSore001]

Howdy,

Just joined, liking the info and informed chats I've been looking at here.

I'm no stranger to mechanical devices and can usually fettle most 2 and 4 stroke stuff OK but an old Stihl 029 chainsaw has got me beat.

It came to me free with no history and needed a bit of TLC - carb cleaned, air, muffler and fuel system sorted, new plug, H and L adjustment, the usual.

Got it running very nicely, a powerful saw with good compression, revs to the max, no smoke.

Problem is it decides to stop once it gets warm, maybe after 2 or 3 minutes maximum of cutting. Just dies. If I hear it beginning to die and try jiggling the throttle it might respond briefly but then dies right away once the revs go up. Will restart if left for a few minutes but dies again quickly. Makes no difference if the fuel cap is loosened so not the vent.

I'm thinking it's the coil but pulled the saw to bits again and the only obvious thing is the pumping diaphragm in the carb is floppy, bulging a little in two places.

Have ordered a carb kit and thinking I might just buy a new coil. But as the saw dies after such a short time it seems unlikely the coil has had time to warm up and get too hot.

Any suggestions?

[bgsengine]

Had one of those. Replace the fuel filter , perhaps. even if they look clean they can be clogged causing flow restriction. another thing to check would be crankshaft end play (of if you have the tester, crankcase pressure/vacuum test) - crank seals can harden and if they wear a bit of a groove (even a few hundred thousandths) into the crank, as the crank shifts it can lose crankcase pressure that is needed to work the fuel pump in carburetor. Also check motor mounts (anti-vibration) and see if they are soft enough to allow saw to flex out and possibly open a crack in the intake boot (or impulse hose) , other than that Ive also had them with fuel line failures (in the ribbed section) that would only show under load (or when testing fuel tank pressure/vacuum to check if tank vent is working right) - even once on a brand new OEM Stihl fuel line!

[ChaneSore001]

Thanks for your advice bgs.

This saw is certainly old but doesn't seem to have had much use. There's no
crank side play and I would expect difficult starting from cold if the
crank seals were leaking. It has no primer bulb and will pop with choke on
after a few pulls then fires up perfectly initially so seems to be getting
adequate impulse and fuel flows freely both ways through the fuel tube.

The piston looks perfect from both sides and compression is fine.

I get a lot of petrol devices given to me and seldom spend any money
getting them running, usually it's just a matter of sorting out what
previous owners have done, or not done, to cause things to stop working.

Just the fact that this saw runs so well when it starts has me interested
in sorting it out, besides it's the most powerful saw in my fleet - our
wood heater is our only heat source and there's endless fallen timber on
our rural property so I do a lot of firewood gathering.

Anyway I'll keep fiddling around and report back if some success ensues.

[bgsengine]

OK just bear in mind I was meaning crank seals can be bad when it warms up (thermal expansion varies between rubber & steel, right?) they can seal well enough when cold (when the saw dies out, does it fire up immediately after, or does it got to cool down first?) If you suspect a coil issue (possibly a loose wire? wires can be broken internally to the insulation and not show outwardly) I'd be running it til it dies then immediately pop the spark plug out and check for spark (could be a bad spark plug too - new ain't the same thing as good) - and if anything suspect there, can also check the coil wire and terminal (pull the boot off, chances are the wire terminal coil comes off with it, check to see if it has not broken or worn through the spark plug wire, may have to pre-drill a new tiny hold just through the first bit of wire insulation to put wire terminal back on, then lube the plug boot with some wax or mineral spirits or something that won't rot the rubber, and try er again... you don't mention what you have in the way of test equipment (vacuum pressure tester? spark tester? Digital Volt Ohm Meter / DVOM? - with the DVOM you can at least check wire resistances and find broken open or shorted wires, etc.)

Could be carb diaphragms are just too stiff from age and needs a new diaphragm/gasket kit...

[KE4AVB]

I can atest to the possible crankshaft seals being a problem as I had an old Husqvarna 37 that was the problem years ago.

[ChaneSore001]

you don't mention what you have in the way of test equipment (vacuum pressure tester? spark tester? Digital Volt Ohm Meter / DVOM?

I have all necessary tools, so far haven't made up anything to block off inlet and exhaust ports to do a pressure test.

The run time before the saw shuts down has been so short the bottom end or coil haven't had time to warm up. When it stops it will restart after a minute or two delay, doesn't need to cool down for more than a few minutes.The carb kit I have ordered should arrive in the mail in a week or so, will see how things go when those bits are installed.

[KE4AVB]

When doing a crankcase pressure test don't forget to a vacuum test on the crankcase. This is important as the crankcase is part of the intake system and that seals will usually seal on pressure but leak on vacuum.

Also be aware spark plugs can fail too. They can be heat sensitive. Use a known good plug while testing.

[Arkie]

If it still does the same after a carb kit.

Change the spark plug first.
Keep a spark plug handy gapped at .030 and a clip to ground it good and when it quits running you can compare the spark to when it runs good.
When it starts dying can you get off the throttle and let it idle or does it just keep on dying.

Start the saw and just let it set outside and idle. See if it will set and idle for 2 or 3 min's.

Also keep in mind if the H jet is set too lean on a chainsaw will overheat when in a constant loaded full throttle cut for longer than 30 seconds. (piston skirt will start expanding into the cylinder wall fast)
On them Stihls you can sometimes buy a replacement carb for less than the kit. Be sure to use the ID info on the side of your carb. STihl uses different model carbs on same model saws. (sometimes 3 different carbs)

Report back.

[ChaneSore001]

Carb kit arrived and has been installed, Found the problem today - fuel line has a split in the ribbed section between the carb and where it goes into the fuel tank, of course it is Saturday evening now and no Stihl dealers around here will be open until Monday.

I cut the line at the split and pushed a short piece of 6mm PVC tube into the cut ends as a join. Might just put the saw back together and see if this "repair" works while waiting on a new line - it is a surprisingly simple saw to work on. I see there are many sellers on EvilBay with parts for this saw which seems to be common to various other models.

Hoping that's all that is wrong.

[bgsengine]

Carb kit arrived and has been installed, Found the problem today - fuel line has a split in the ribbed section between the carb and where it goes into the fuel tank, of course it is Saturday evening now and no Stihl dealers around here will be open until Monday.

I cut the line at the split and pushed a short piece of 6mm PVC tube into the cut ends as a join. Might just put the saw back together and see if this "repair" works while waiting on a new line - it is a surprisingly simple saw to work on. I see there are many sellers on EvilBay with parts for this saw which seems to be common to various other models.

Hoping that's all that is wrong.

Heh. shows how forgetful one can be after being out of the business even a couple years.. I shoulda suggested looking for that as it was one of the *MOST* common things I would see on those Stihl's that came through my shop. Can't believe I didn't even think to suggest checking that. LOL! (Though in my defense you did say fuel system sorted, so one would assume meaning fuel lines & filters, tank vents, etc) But no your patch probably won't work any better than the cracked line - it'll still leak. Those cracked hoses - (Also common in the Pulse hoses that operate fuel pump, which WOULD have been found on a crankcase pressure test, and symptoms similar to aforementioned crank seals)- are typically rotting apart on the inside so they end up clogging the carburetor filter screen. Just have to bite the bullet and wait for a replacement (or rob it off another 026, 026, MS-290, Etc)

Bear in mind most of the Stihl parts you find on Ebay or Amazon or Elsewhere are generally either counterfeit, Aftermarket, or New Old Stock . Stihl has very strict rules on its dealers that they cannot sell parts online, some dealers get around that by cutting in a "middleman" seller, but that's usually the smaller shops that need to boost their parts inventory turnover to stay in business and maintain their discount levels - There's seriously no profit to it otherwise due to competition - Others that are genuine may be stolen inventory or buyouts of closed-up dealers old inventory, etc.. All the rest are pretty much Aftermarket (but some try to sell as genuine parts, and thus they are counterfeit)