# Husqvarna 350 chainsaw



## rickyjoseph701 (Oct 18, 2012)

Can someone explain to me what is a decompression valve (on this saw) and also how does it work. Got the saw from a friend and he didn't know what it the valve was for or how to use it either. The saw does not start , however it does have spark, compression , gas and a clean , rebuilt carb. Any help on this saw will be appreciated. 
Thank You.


----------



## paulr44 (Oct 14, 2008)

The deko valve (as we call them), is just that. It provides de-compression during pull-over, and when the charge in the combustion chamber burns, the rapid expansion of gasses forces the valve (built into the design) to close. It's valve extends from the blue button down into the body, and has a typical 4-stroke style valve head (a cone shape).

You can pull the valve out to close it which should give you near to full compression. IF THEY LEAK BADLY it can cause engine damage by allowing a compression and combustion loss. We have seen this, and you can really only test them with by doing a crankcase pressure test.

It's unlikely that this is the source of the problem, unless it's stuck open. *Even so, it'd fire, run badly for a few seconds and die*.

Take some good carb. cleaner (must be flammable) or raw gas (or even just use pre-mix alone with nothing else), and put it and some WD40 into the carb. venturi with the throttle held open. Then try to start it, which may take 5 to 10 pulls, no choke necessary. You're only trying to see if it'll fire, not run with this test.

When you say it has compression, is that based on a calibrated forearm or a compression tester? Min. should be like 120 lbs. depending on the engine displacement (with the deko valve pulled out).

Spark should jump about 0.150" to 0.180" gap. Rule of thumb is 1KV per 1 MM.


----------



## rickyjoseph701 (Oct 18, 2012)

*Husqvarna 350*

I did this and it did fire, ran for a few seconds and died. Any further information or what I can try, want to get this thing running before to much longer. Thanks for your in put.


----------



## paulr44 (Oct 14, 2008)

It could be a number of things, from a cracked fuel line to a plugged up carburetor, but most likely it's a fuel delivery issue. What I'm saying is, you've determined the engine is capable of running, but it could have a vacuum leak, or it has a fuel del. issue which is the most likely problem. Look into the fuel tank with a flashlight and see if the fuel line isn't broken off, as can happen on husky saws with plain lines. If it has the black rubber looking lines, check near the carb. for cracks. If all looks good there, you can determine if the carb. is getting fuel by removing the fuel line from the carb. and seeing if fuel (from natural tank pressure, although stale fuel won't make pressure and you make have to shake up the saw to make pressure) squirts out. If so, then the carb. is prob. clogged up.

If you're unfamilar with carb. rebuilds, you may want to price a new one...some are very reasonable considering a rebuild isn't guaranteed to work. Take the carb. numbers and google them. Look for brand - walbro or zama, WT, HD, C1U, C3 and then the spec number after that to get the whole number. Eg. WT-223, HD (or HDA) -45, C1U-45A.


----------



## rickyjoseph701 (Oct 18, 2012)

I replaced fuel lines and checked the carb again and it still does the same thing, runs a few seconds and dies when carb cleaner is sprayed in the carb.


----------



## paulr44 (Oct 14, 2008)

I don't know what else to say. If it runs on a prime, as I said that's promising. Yes, it could have a vacuum leak, but USUALLY that leak isn't bad enough (it could cause a major failure though) to prevent it from running at all. There are a lot of problems leaks can cause on a 2-stroke. The fuel pump pulse line for instance. But even if that were the problem, it'd still start on full choke with a throttle in partial-open locked position.

Have you done a crankcase pressure-vacuum test?

Have you priced a new carb? Given our labor rate in the northeast, if a carb. is about $70 or less it's a no-brainer - just replace it and be assured that fuel delivery is guaranteed.


----------

