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029 Super won't stay running

Started by demulsion, March 10, 2017, 04:43:55 PM

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demulsion

I've been doing lots of reading and trying things, but the problem persists.
I have a lightly used Stihl 029 Super that was running great, and then randomly died mid cut. It would re-start, but die again in 15-20 seconds. So far I have replaced the fuel line and filter, spark plug, and air filter (because it was probably due for a tune up anyway), cleaned and verified the pulse line is clear and isn't cracked, entirely disassembled and thoroughly cleaned the carb, removed and checked the muffler for blockage, and tried running it without the fuel tank vent line, as well as running it with the fuel cap loose. I peered in the cylinder bore while the muffler was off, and there is still cross-hatching on the cylinder wall.
It still starts as easily as always, but I can't get it to stay running for more than about 30 seconds. Idle or WOT doesn't matter, it just bogs down and dies. It will restart right away without much trouble.
I'm stumped (pun intended). Any more ideas would be appreciated.

Kbeitz

Did you check the gas tank vent ? Some are in the cap.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

dougand3

"entirely disassembled and thoroughly cleaned the carb"

How were the diaphragms? If stiff, saw won't get the proper amt of fuel.
Husky: 372xt, 272xp, 61, 55 (x3)...Poulan: 315, 4218 (x3), 2375, 2150, 2055, 2000 (x3)...Stihl 011AVT...Homelite XL...Saws come in broken, get fixed or parted, find new homes

demulsion

I don't recall the diaphragm being stiff, but didn't think to check them specifically.
Part of what throws me off is that it first started acting up mid cut...

joe_indi

Try disconnecting the black wire from the coil. Have you replaced the air filter recently? If yes, try starting without the air filter. Check whether the strainer on the pump side of the carb is partially blocked.the only other possibility that I can think of is a leaking jet valve (if the seals have not failed)

demulsion

I pulled the carb apart to double check the diaphragm, and it was still in good shape like I thought. Put it back together, and it is running great now?!

Happy to have my saw working again, but bummed I don't know what I did so that I don't end up stuck again...

dougand3

Good it's running. I would guess either the metering or fuel pump diaphragm wasn't seated properly. After re-do, it is.
Husky: 372xt, 272xp, 61, 55 (x3)...Poulan: 315, 4218 (x3), 2375, 2150, 2055, 2000 (x3)...Stihl 011AVT...Homelite XL...Saws come in broken, get fixed or parted, find new homes

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