Husqvarna 394 won’t stay running/barely starts

[TBE]

Hello all,

I am at a complete loss- my Husqvarna 394 chainsaw will start but immediately dies. It is a 1998 model.


I have already tried the following:


New Gas line
New Fuel filter
New Fuel tank vent
New tank vent filter
New Gas cap
Put carb kit in it
Cleaned the carb
Air filter is clean
Spark plug gap is fine - to specs
New spark plug
Gets spark
Decent engine compression, according to the shop (120)
Muffler is clean
New gasket between carb and intake opening

Took it to the shop and they said it isn’t getting enough fuel (hence the overhaul of the fuel system I did) and wanted to charge me $150-200 to figure out the problem and fix it so I said “to hell with it, I can do this”- but I’m starting to give up.

I tried adjusting the L needle on the carb multiple times (started with it 1-1.5 turns out as the manual suggested), but it won’t stay running long enough to make the adjustments. The metering lever is set to just about level with the carb body. It is a Walbro wj70 806 carburetor.

The problem seems to intensify when I’ve been trying to start it for a while - aka when the engine is hotter. It usually always starts with the choke on and sometimes even stays running longer -a few seconds longer- (revving high of course ) until the choke is pushed in and it dies. Also, the decompression valve doesn’t always pop out even after it ran for a couple seconds. Took that out too and cleaned it, seems to be functioning well.

Any and all help would be MUCH appreciated! Thanks!

 

[HarleyT]

Pop on a new carb.

 

[TBE]

I thought about that. I just wanted to make sure that i eliminates everything else before dropping $80-90 on a new carb... I did however clean the whole thing and every opening/jet/hole etc was letting compressed air/ carb cleaner through fine. Do carbs just go bad? Could it be something on the inside of the carb that I would never get to?

 

[decableguy2000]

Gasket blocking impulse passage? Diaphram hooked on the lever? Gasket and diaphram in the correct order? Compression should be enough, but on the low side?

 

[Derrick Sawyer]

I wouldn't do anything until i got a good look at the piston thru the exhaust or take the spark plug out and look at the cylinder wall above the exhaust port with a pen light to make sure there isnt scoring, then a pressure and vac test would be next. Compression a bit is the low side if the reading is correct.

 

[pioneerguy600]

This first.^^^^^^^^^^^, all else is just guess work.

 

[rupedoggy]

air leak

 

[atpchas]

Also, the decompression valve doesn’t always pop out even after it ran for a couple seconds.

Something is wrong if the decomp doesn't pop as soon as the engine fires. Try a new valve or just plug the hole with the correct sized bolt.

 

[huskyboy]

120 is low compression. around 150-165 is usually what they do stock. I’d be pulling the muffler and taking a look...

 

[TBE]

I’m going to take some photos of the cylinder and piston tomorrow and post it for y’all to look at.

I also thought it might be an air leak but where?! I replaced the gasket between the intake manifold and cylinder about a month ago and just looked at it again and seems fine.

 

[Derrick Sawyer]

Since that saw is 20 years old, air leak could be from crank bearing seals, case gasket, cylinder base gasket, impulse line, intake manifold (solid piece which can form small cracks), decomp valve, spark plug if not seated correct. Hopefully there is no scoring and its something simple like someone else thought about the decomp valve (make sure its tight and pull it all the way out when checking compression and starting), and i believe the oem ones had a blue button, i always replace with oem, had a bad batch of aftermarket decomp valves, not worth the trouble. I would get a good compression testor for yourself, hopefully its at least 140. Is this saw new to you? Has it been sitting a long time? Stored with old fuel?


I rarely use my 394 but when i get to 36" oak, its noticeably more powerful than my 660's and less vibration.

 

[Deleted member 117362]

As said above. 1. Pull muffler and check p/c. 2. Plug decompression and vac/pres check (check compression again looking for 140-150). 3. Try a different spark plug (you can buy a bad one). 4. Check impulse to make sure it's clear. 5. Try a new carb. 6. Pinched fuel line. 7. Coil may be breaking down. 8. Stop and repair what is wrong with saw. 9. You can always send it to me, they are strong runners.

 

[TBE]

THanks for all ideas, guys!

I attached photos of the piston and cylinder (as much as I could fit my phone in there).

The more I read about it, the more I’m leaning towards doing the vacuum and pressure test. The choice of “good” testers is overwhelming online though. I found one, the Mityvac 8500, that seems to be pretty good but I’m not sure if it will do the job for me. Does anyone have any suggestions on a good combination vacuum/pressure tester?

 

[atpchas]

IMHO, the Mityvac 8500 is the "gold standard." They're not the least expensive, but they do a great job and will do both pressure and vacuum, unlike some other testers.

 

[HarleyT]

IMHO, the Mityvac 8500 is the "gold standard." They're not the least expensive, but they do a great job and will do both pressure and vacuum, unlike some other testers.

 

[Gord404]

Sometimes the intake block that bolts your carb to your cylinder can develope a crack and let air in so if you do a leak down test best to put your rubber block off between that and the carb, and the other between the muffler and cylinder - vac-pressure test is a good way to assess what may be or may not be wrong with your saw- takes a lot of guesswork out of it- lots of info -how to on utube.

 

[TBE]

Any thoughts on the condition of the piston/cylinder based on the pictures? (Again, I realize they aren’t perfect...)

 

[TBE]

Also- couple more questions:

When looking up parts for this saw I usually use the diagrams found on ereplacementparts.cm and they have a few different options to choose from based on the year of this saw. How would I determine which one to look at? Does that even make a difference?

While researching new pistons and cylinders (in case I will need it- prolly a good idea either way) I am having a hard time finding one for a 394. I’m guessing it’s because of the age of the saw. I did find a meteor conversion kit (with everything included) for $200 on eBay that would let me put a 395 p/c on it. What do you all think about doing that? Is it worth it other than the availability of parts? Is it relatively easy to do with reliable results? Can I use the same carb with a 395 p/c (given that it’s good)? It has a Walbro WJ70 on it right now which is no longer available...I think the WJ71 is the one that is the most comparable...would those two work well together? The 395 p/c and either the WJ70 or 71?

 

[HarleyT]

Take your carb apart again, and put up some pics. Also a pic of your metering lever.

 

[TBE]

Since that saw is 20 years old, air leak could be from crank bearing seals, case gasket, cylinder base gasket, impulse line, intake manifold (solid piece which can form small cracks), decomp valve, spark plug if not seated correct. Hopefully there is no scoring and its something simple like someone else thought about the decomp valve (make sure its tight and pull it all the way out when checking compression and starting), and i believe the oem ones had a blue button, i always replace with oem, had a bad batch of aftermarket decomp valves, not worth the trouble. I would get a good compression testor for yourself, hopefully its at least 140. Is this saw new to you? Has it been sitting a long time? Stored with old fuel?


I rarely use my 394 but when i get to 36" oak, its noticeably more powerful than my 660's and less vibration.

I bought the saw used about 4-6 months ago and milled quite a bit with it after a major cleaning and minor repairs (new air filter, air filter housing, fuel filter etc). Intact I was milling a 30” walnut log couple weeks ago and it worked like a dream with a 42” bar! Smooth as they come, didn’t shut down once, didn’t overheat nothing. I’m running 40:1 with the Husqvarna 2 stroke oil and 96octane gas in it.

Honestly it has been a great saw for it’s age, but it has me stumped at this point.