Stihl MS440 Magnum won't stay running

[Skillet]

I've had this saw for 6 years and it's been bulletproof - until yesterday.  On Monday I fired it up after a few month long sit - it was balky at first but cleared up and ran like a champ.   Yesterday when I went to fire it up it would always fire on the full choke on the 2nd pull, then fire on the 1/2 choke on the 2nd or third pull and keep running for just a few seconds.  Tried to massage the throttle and it seemed like no fuel.  Eventually, I couldn't get it to fire at all.    Pulled the plug and it looked good and clean, with good spark.

Any ideas?  I'm thinking fuel pickup plugged or tank vent blocked?  Gas has been sitting for a while, but it is the same fuel I used yesterday and it ran fine.

[rtspring]

Check the fuel line, sometimes they get disconnected from either the tank or carb.

[Woodchuck]

Ethanol gumming, get the carb gone through and use stabil or drain gas before parking for the winter. A little trick I do is to run 110 octane race gas, runs cooler, is leaded, no ethanol. 

[whacker1]

Ethanol gumming, get the carb gone through and use stabil or drain gas before parking for the winter. A little trick I do is to run 110 octane race gas, runs cooler, is leaded, no ethanol. 

[Skillet]

I ran it dry before I put it up a few months ago - I learned the hard way about letting ethanol fuel sit for any length of time in power equipment! 

I will try and get my hands on some leaded AV gas.  I used to buy it for a street/drag car I had back in Spokane from Felts Field.  Does anybody know if they'll sell it in containers at Paine Field?

[Heredoggydoggy]

I had the same problem with a chainsaw that hadn't been used in a few years.  Turned out that the diaphragm in the carb got old and cracked, and wouldn't pump gas to keep the saw running.  Like losing the fuel pump when that happens.

[Woodchuck]

I ran it dry before I put it up a few months ago - I learned the hard way about letting ethanol fuel sit for any length of time in power equipment! I will try and get my hands on some leaded AV gas. I used to buy it for a street/drag car I had back in Spokane from Felts Field. Does anybody know if they'll sell it in containers at Paine Field?

AV gas can be hard to get a hold of now for whatever reason. You can buy a 5 gal can of VP110 from just about any local bulk fuel and oil distributor, it aint cheap but I will swear my saw runs longer per tank on it as well. Also try Amsoil 100 to 1, 2 stroke oil, I still mix it a little rich like 80 to 1 but the saw loves that stuff. Is good for any 50 to 1 application. 

[woodswalker]

Another option is to check with your local Cenex Coop, most of them handle at least one tank of no-alcohol gas.  I know that the one in Snohomish does, as well as a station in Marysville.  ALL my power equipment gets alcohol-free gas.  I also mix with Stihl synthetic oils only.

[Skillet]

Great tips guys.  I'll check the co-op in Everett to see if they have it, and if not, I'll go find the VP110.  I have two gallons of 2 stroke oil in the shelf right now that I'd like to use up before I spring for the Amsoil, though!

[Woodchuck]

 

[whacker1]

http://pure-gas.org/index.jsp?stateprov=WA

This web-site might be helpful, it shows you the stations that have been reported by others as offering ethanol free gas.

i have found the list to be relatively accurate.

[PolarBear]

Ethanol gumming, get the carb gone through and use stabil or drain gas before parking for the winter. A little trick I do is to run 110 octane race gas, runs cooler, is leaded, no ethanol. 

I found that running only non ethanol gas in all my power equipment (saws, weedeaters, tillers, mowers, outboards, etc) has eliminated all of my start up problems.  Ethanol will eat and dissolve rubber and anythng with resin (fuel tanks and lines).  Clean out your tank, check your filter, try fresh ethanol free fuel and put an additive to clean out the system.   

[mrgoodwrench]

Check the fuel and impulse line, they get old and collapse over time.  Or sell it to me for $100 !!

[iusmc2002]

I fixed a saw for a guy a couple days ago.  He said it was a real bear to start, he worked up more of a sweat getting it started, than actually cutting wood.  I took it apart and played with the plug, carb and air filter.  I put the air filter back onto the carb with the side that was previously out, on the inside and it started right up.  I let it cool down for 30 min to be sure it wasn't just a gimmick, flipped the foam filter over, so that it was the way it was when I started, and it wouldn't start AT ALL.  Flipped the filter back around and started again and again, no prob.  I realize Stihl's don't have foam filters like that, but have you tried starting it without the filter on?

[Skillet]

Update:

Bought a new fuel pickup and carb kit.  Replaced pickup.  Old pickup didn't look to be clogged and the fuel line looked pretty good to me.  Cranked saw a few times and it took off for a bit, but still hard to keep running.  Kept it running long enough to cut the last of my rounds. 

After dark I took it into the garage and started taking it apart.  Opened the fuel filler cap again and there was a tiny "whoosh" of air going in... so took out the fuel tank vent and saw that it was PLUGGED SOLID.  Fine alder dust had gotten in and filled every little hole in the top of that thing.  Took the vent apart and cleaned it.  Did a general clean-up of the saw, cleaned and oiled the filter (it was pretty full of alder dust, too), and put 'er back together.  Didn't fire it off last night - the neighbors would have been a little pissed as it was 9:30... 
I'll report back tomorrow with the results!  If that isn't it, then I'll get a little deeper into it and check some other things you guys have suggested.  Probably more of that alder dust in there somewhere.  That stuff is like putty under the right conditions...

Thanks for everybody's suggestions here - especially mrgoodwrench's very generous offer to relieve me of my troubles and give me $100 to boot.  That is the kind of offer I just wouldn't expect to get anywhere else 

[Skillet]

So the fuel tank vent was it.  Fired it up last night, instantly idled down to correct speed and had instantaneous throttle response.

Thanks again all -

[Woodchuck]

good news man 

[BigGoonTuna]

pull your carb off and put a dab of grease on the impulse line.  give the rope a couple yanks - if it spits it out, you're good, but if nothing happens, it's probably got a crack in it or pulled off the nipple on the crankcase(fairly common).

[dbor]

Feul filter in the tank? Diafram, or maybe the sparke arester in the muffler.... it is a screen in the front of the muffler?? Just take it out and clean it.... don't use fuel... Good luck