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I've got a husqvarna 440e that's all over the place. One day it'll run great, the next day I can't get it running at all. Sometimes it's way lean and will take off at idle, sometimes it's way rich and will literally dump raw gas out of the exhaust.

I can usually tune it on a given day, but it takes 30+ minutes of playing around with the hih and low jets to get it to run properly and also idle without dying. The next day, it'll be completely out again.

I've disassembled, ultrasonic cleaned, and rebuilt the carb, as well as the exhaust. Opening up the exhaust leaned the saw out quite a bit, which made it happier (it was rich that day), but the next day (today), it's way rich again. Air filter is clean.

Plug gap is right on spec (0.020"), I start my tune every day on 1 turn out (way leaner than stock, but where it seems to start being happy.

The only thoughts I have left:

There's a vacuum leak somewhere. This doesn't seem right since I've built the carb and the seals all look fine. The fuel bowl is leaking fuel into the air box, and causing it to run rich if it's left sitting (most day it's richer than it was the last day). This is something I can check (just crossed my mind) but doesn't feel right Are there any other spots I can check? When it's happy, it's a great saw. When it's not, it's quite frustrating.

Update

I pulled the air box apart after an evening of storage. The tank (full when I stored it) is now half empty, and the airbox and air filter are soaked with fuel. It seems that the fuel bowl needle does not hold a full seal and storing the saw hanging from its handle causes the saw to run terribly until the air filter dries.

I'm not sure it's feasible to replace the needle, so I will store it flat for the time being

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  • This is a 2-cycle chainsaw? Yes, I understand most chainsaws are, but just making sure. Nov 8, 2023 at 12:11
  • Yes it is - a standard 2-cycle with a slightly ported exhaust (leans it out but I did the tune after the mod). Nov 8, 2023 at 12:35
  • Have you checked the reed valve to ensure it's not loose/moving? Nov 8, 2023 at 12:43
  • I have not. I guess I forgot that these aren't just open port 2 strokes. I'll check the reed block and see if there's issues there Nov 8, 2023 at 12:55
  • I'm not sure that it does have a reed valve. Most small 2-strokes do, though. This could also be the vacuum leak like what you're talking about. Nov 8, 2023 at 15:39

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It seems the main issue here was in fact a fuel leak. The way the saw was stored (hanging vertically from the handle), it would leak gas into the carburetor through the fuel bowl needle if the tank was above about 50%. This would soak the air filter and fill the air box with gas, causing an extreme rich condition.

I would then tune it way lean, run about half a tank of gas, and the next day with no fuel leak it would run extremely lean.

The short-term solution is to store the saw flat. Long term, a new carburetor or at least new fuel bowl (I guess it's a diaphragm) needle will stop the leaking.

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