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Author Topic: Sthil MS440 question  (Read 346 times)

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Offline WV Sawmiller

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Sthil MS440 question
« on: November 14, 2017, 08:38:57 pm »
   Ok. I confess - I'm no mechanic. I do have a question about my old 440 Sthil hoping somebody can help with.

    I was cutting some small firewood yesterday and about halfway through a tank of gas it suddenly revved up like it typically does just before it runs out of gas. Kept running through another cut or two then stopped. I thought was out of fuel but when I opened had at least 1/3 tank of gas. I topped it up and could not get it to crank. It still seems to have compression in that the cord does not just easily pull out nor is it frozen up.

   Any suggestions on trouble shooting tips? My gas can was nearly out of fuel  and I'm inclined to just empty the saw tank and ditch the rest of the gas in the can and start with fresh gas. Would bad fuel cause the saw to rev up like that and run at a higher idle for a while?
Howard Green
WM LT35HDG25(2015) , 2009 4wd Dodge PU, Kawasaki 650 ATV, Sthil 440 & 441, homemade logging arch (w/custom built rear log dolly), JD 750 w/4' wide Bushhog brand FEL

Dad always said "You can shear a sheep a bunch of times but you can only skin him once"

Offline old guy

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Re: Sthil MS440 question
« Reply #1 on: November 14, 2017, 10:03:14 pm »
I would immediate pull the muffler & take a look at the piston, sounds like an air leak to me & a fried piston.
 When a saw starts high revving by itself always stop to find out why.

Offline WV Sawmiller

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Re: Sthil MS440 question
« Reply #2 on: November 14, 2017, 10:18:46 pm »
   Thanks. I'll try that. What am I looking for? Discoloration or bluing or such?
Howard Green
WM LT35HDG25(2015) , 2009 4wd Dodge PU, Kawasaki 650 ATV, Sthil 440 & 441, homemade logging arch (w/custom built rear log dolly), JD 750 w/4' wide Bushhog brand FEL

Dad always said "You can shear a sheep a bunch of times but you can only skin him once"

Offline sawguy21

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Re: Sthil MS440 question
« Reply #3 on: November 15, 2017, 04:19:56 am »
If the piston is damaged you will see deep scratches in the skirt.
old age and treachery will always overcome youth and enthusiasm

Offline johnny newburgh

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Re: Sthil MS440 question
« Reply #4 on: November 15, 2017, 05:25:43 am »
Do you have a vacuum pump? Like a mighty vac for bleeding brakes? I was just trying to diagnose my saw and I found out through Youtube videos that you can test several things with vacuum or pressure test. You can check If fuel cap Is venting, check fuel line for leaks, check carburetor seals and fuel needle and primer bulb, Also do vacuum and pressure test on case to check crankshaft seals. Air leak on base gasket and leaks on cases,Look at some videos some real good stuff on there.

Offline sawguy21

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Re: Sthil MS440 question
« Reply #5 on: November 15, 2017, 05:39:46 am »
X2 It's a really good idea to find why it failed before tearing down and throwing expensive parts at it. There is no point tearing up a new p&c.
old age and treachery will always overcome youth and enthusiasm

Offline limbwood

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Re: Sthil MS440 question
« Reply #6 on: November 15, 2017, 07:16:45 am »
you might just have a plugged fuel filter.

Offline WV Sawmiller

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Re: Sthil MS440 question
« Reply #7 on: November 16, 2017, 05:05:04 pm »
Old Guy & Saw21,

   I pulled the muffler and did see some significant scarring on the cylinder in there. I assume that is not good and I have a sick saw. I will try to get it to my saw doctor the next time I am going that way. He had quit but talked like he was going to start back up. The last time I took it to the dealer they wanted the price of a new one to repair this one.

   I did empty the gas out of the saw and what little was in the can and put some fresh gas in from my outboard motor tank which I always use up this time of year - same mix for outboard, saws, weedeater & leaf blower. I'll start with fresh gas in the outboard next Spring.

   I pulled a few times and it sputtered then cranked. I did not try to saw anything with it yet so I don;t know how much compression loss I may have.

    Thanks for the suggestions and pointers.


Howard Green
WM LT35HDG25(2015) , 2009 4wd Dodge PU, Kawasaki 650 ATV, Sthil 440 & 441, homemade logging arch (w/custom built rear log dolly), JD 750 w/4' wide Bushhog brand FEL

Dad always said "You can shear a sheep a bunch of times but you can only skin him once"