Stihl ms 440 not running well when cold

[outdoorfan]

Hi fellas,

I could use some advice if any of you have experienced this. I'm about to tear into it, but I'm looking for some pointers, if possible. My 440 has been gradually running worse and worse throughout this past fall, as the weather has been turning colder.

What happens is that is cuts out under high revs. It'll die if I don't immediately let off the throttle. There were times that it would run better once I had been running it for awhile, but then I noticed that after refilling the gas tank, it would act up again, even if the saw was warm from use. It would also take a long time to start it from a cold start, like it wasn't getting enough gas.

Last night I put it in my heated shed in preparation to work on it. Just for kicks and giggles, I fired it up this morning to see if being in the shed overnight made a difference. It started up and ran flawlessly for 1 minute or so, when I shut it off. So then I left it out in the cold for a few hours. Sure enough, it started cutting out within 10-20 seconds of revving it up. I put it back into the shed to warm up for a few hours again. Started it up, and it runs fine.

I have neglected maintenance on this saw. The fuel tank breather, if it has one, has never been replaced by me. I don't know if that is a possible culprit. I've never gone through the carb or changed any gaskets. I can do all those things, but if someone can clue me into the likely culprit, I'll start there.

Thanks!

 

[HarleyT]

Need to go through the fuel system properly first.

 

[outdoorfan]

Ok. So, I take that to mean gas tank, and then carb.

 

[HarleyT]

Well, fuel line could be bad, cracks or getting gummy. Which in turn might mean dirt/gunk in the carb.. The carb diaphrams are likely stiff,
gunk clogging jets. Impulse line may be bad too, which should be looked at while the carb is off.

 

[HarleyT]

Fuel tank breather is not likely the problem...

 

[outdoorfan]

Ok, thanks. So I'll go ahead and order up a carb kit. I'll go through it and replace that diaphram, which I agree is probably dot doing so well.

 

[alexcagle]

It might be as simple as a clogged fuel filter that as it gets colder, the oil in the fuel becomes thicker, and has difficulty flowing through the filter media or membrane, and then the old fuel hose sucks shut.
Could be a neglected spark plug misfiring from a .050" gap causing the spark to occasionally jump spark to the plug base.
Try the simple obvious cheap things first.

 

[outdoorfan]

Ok. Thanks for those wonderful tips. Will do that before the carb kit.

 

[crabby cooter]

whats the temp outside?

 

[outdoorfan]

Temperature was about 20 degrees earlier today. The saw has been getting more and more temperamental because back in September there were early signs of this issue, yet it still performed okay in warmer weather.

 

[mountainlake]

Did you tune it for cold weather? Saws need more fuel when cold. Steve

 

[outdoorfan]

I'm pretty sure it has nothing to do with that because I've had this saw for 7 years, and it's not given me any trouble llke this.

I will order parts, dink around with it, and then report back when I get it solved.

Thanks!

 

[mountainlake]

Your not getting the best performance out of your saw if you don't adjust for temperature changes, I have to adjust all of mine more fuel in the cold and less when hot. Steve

 

[Khntr85]

Have you peeked at the piston.... if you pop off the muffler can you get us some pics?????

 

[blsnelling]

They always need more fuel as the weather gets colder.

 

[outdoorfan]

I'm not doubting that a tad more fuel will make the saw run better in the cold, but that's not what's happening here, I'm pretty sure. The problem that I'm having is seemingly much worse than what a slight fuel adjustment will achieve. Nevertheless, I will see, for the heck of it, if tweeking the jet will make any difference.

 

[outdoorfan]

I will not likely have the parts in for several more days, so I'll report back when I've hopefully found the problem.

 

[blsnelling]

Do yourself a favor and pull the muffler cover before using it again.

 

[outdoorfan]

I will do that, Brad. Thanks also to Khntr85 for that insight. I will look at that today and report back. Somehow I didn't equate my problems with the possibility of a scored cylinder.

 

[RiesePING]

I'm not doubting that a tad more fuel will make the saw run better in the cold, but that's not what's happening here, I'm pretty sure. The problem that I'm having is seemingly much worse than what a slight fuel adjustment will achieve. Nevertheless, I will see, for the heck of it, if tweeking the jet will make any difference.

Well if it ran flawlessly when you started it from your heated shed and then runs like crap when it's exposed to cold air temp, I think the easiest troubleshooting you could do would be just to quick richen it up and tune it outside in the cold...would take 1 minute and then you'd know for sure. But I guess it sounds like you already have your mind made up.