Homelite chainsaw stalls when I open throttle

[rszimm]

So I've got a little ut10540a 35cc chain saw. It doesn't get a whole lot of use, but I've been using it a LOT the past week or so. One thing I've noticed is that sometimes I'll come out in the morning, fire it up and it'll just run like a dream. Other times it'll fire up fine and stall immediately with a big throaty WAAAAH when I pull the throttle. When this happens I'm in for 10 minutes of fighting with the thing, pulling the choke, pushing the choke back in, emptying the gas, putting new gas in, and yanking on the starter. Every time the same thing. Then it seems something just "clicks" and it starts and runs fine.

Here's another strange thing. This stalling thing doesn't only happen some mornings. Sometimes I'll put the saw down and turn it off while I do something else. 90% of the time it'll fire up fine when I come back, but that other 10%, I'm back to the throaty stalling problem. This is why I'm very hesitant to adjust any of the three carb screws. When it's running it's fantastic. It'll idle forever. It'll rev great. It'll start easy. Then it goes into throaty hell mode and I can't touch the throttle or else it'll stall immediately.

FYI, I just replaced the fuel lines. I have noticed that the gas tank sometimes gets a bit of pressure in it that is released when I crack the cap. I pulled the little check valve in the cap, cleaned it well and tested it. Seemed to work fine. Although I think that's more to prevent a vacuum in the tank rather than a pressure situation.

 

[banditt007]

You are correct there is nothing to vent pressure, only to relieve vacuum. Pressure in the tank is completely normal.

To me it sounds like the diaphragms in your carb are stiff and getting stuck. Making for a lean condition when it stalls after its running, and making for just not getting enough gas in it to fire when it happens in the mornings. One thing you can do is is check for spark, when it acts up but it sounds completely like a carb issue. I wouldn't even bother with a carb rebuild kit, you can usually buy Chinese carbs for really cheap and often they include other things like purge bulb/fuel filter/spark plug/gaskets/fuel line ext....all for $20 or less. Check ebay/amazon.... I just looked....$14 shipped and includes everything I mentioned. Usually the purge bulb/gaskets/carb are good. The spark plugs are usually cheap knock offs that I wouldn't really trust.

Good luck. reply back how it all works out.

 

[Conquistador3]

Just two questions.
First, how old is the saw?
Second, how long do you let it sit idle with fuel in it?

 

[rszimm]

The saw is probably 10 years old. I've let it sit for long periods of time with gas in it. I always use stabil, but I know that only goes for a month or two and I've definitely let it sit for years between starts. Anyway, it's been run every day for the past 10 days and the symptoms have not really changed.

 

[Conquistador3]

Your carburetor's membranes have gone stiff from being exposed for too long to various chemicals present in oxygenated (ethanol) unleaded fuel. It happens on everything using a membrane carburetor sooner or later: by using fuel stabylizer you have bought your saw some time but remember the best form of long-term storage is to drain the fuel tank and "run the saw dry", meaning turning it on after draining the fuel tank and letting it idle until it runs out of fuel.
Stiff membranes mean the carburetor has problems pulling fuel from the tank, until it will eventually stop altogether.

You will definetely need a new carburetor: apparently nobody bothers with a rebuild kit for the une used on that Homelite. They are $15 or so on eBay.
You may also need new fuel lines and perhaps a fuel filter, but start by replacing the carburetor and see where you go from there.

 

[rszimm]

Thanks. I ordered one yesterday from amazon for $15. Should be here later today. I'll let you know how it turns out. Now if only I can get the oiler to not drain the tank after about 20 minutes of running!

Do they make fuel line that doesn't deteriorate in 24 months or so. I swear I've replaced the fuel line on this thing 3-4 times over the past 10 years.

 

[rszimm]

So just an update. I popped in the new carb and things seem to be running smooth. The carb I got had to be modified slightly to get it to work (the choke had a detent in it which caused it to stay open when you pulled the throttle....easy to remove the detent ball and spring. It also had a copper tube that was longer than the original which I just hacksawed off).

 

[banditt007]

Cool, nice fix for $15 huh haha. Updates are highly under rated, always good to see how everything turned out.