MS440 running rough and stalling out

[Evanrude]

Ok, since getting the newer 440, I'm ready to really tear into the older one to figure it out. It never did really run right.

Here's the series of problems...

At first, sporadic idling along with random stalls. The stalls are usually at idle or part throttle and are instant, no warning, no flutter, it was just like I flicked the switch to 'off'. The stalls occurred weather the saw was sitting right side up, on its clutch or starter side. Adjusting the 'L' screw was like trying to thread a 5/8" rope through a fish hook. A very small adjustment (1/32nd turn) either way and she would stall out. So I took the carb off, cleaned it out. Replaced carb, 'L' was easier to adjust, may have gotten 1/8th turn either way out of it before stalling. Talked to my buddy at the dealer, he said try and soak it overnight, remove all jets and adjustment needles. Put a new fuel and pickup in as well. After that, the 'L' was better, but still not right. Saw still randomly stalled out, not quite as much. So next thing I did was installed a new carb kit. The 'L' screw is normal compared to my other saws. It idles 'OK', still not right, a little rough. Only stalling out when the starter side is up, even with full tank of gas. (I've been thinking seals in the back of my mind since day one, but it was too random to be the culprit, or so I thought). When it stalls out it just quits, no increase or decrease in engine speed.

I guess I should just have my dealer do a vacuum/pressure test and see where it goes. Would the impulse line be causing this? It just seems odd because with a crank seal going bad, I read on here that the engine will usually race once on its side. Could this have something to do with the coil, as it almost seems to be an ignition issue. This is the first saw I've dug into so I really am having a hard time on where to start.

Sorry for the book, but I wanted to be very clear on whats going on. Thanks for all your help in advance!

Evan

 

[Nailsbeats]

I just bought a used 440 that is stalling randomly at idle too. I haven't looked at it yet cause I just found out about it this weekend. Looking forward to the replies you get.

Man I love them 440's!!!!!!!!!!!!!!!!!!!!!!

 

[pioneerguy600]

It does not sound like an air leak to me as they usually cause the engine to rev up not stall . If the engine will run WOT then it sounds like its getting gas and should be getting enough to idle. Did you change the gas line or airfilter?If you get it vac tested have them do it with the impulse line and the boot on as they may be cracked but not likely in this case. I have seen the kill switch wire grounding out and stopping the saw but that happens at WOT and idle also. Did you change your sparkplug for a new one? An old plug has caused a lot of saws to stall while idling in my experience and sometimes a new plug is all it takes.
Pioneerguy600

 

[Evanrude]

New air filter and plug.

 

[THALL10326]

Ok, since getting the newer 440, I'm ready to really tear into the older one to figure it out. It never did really run right.

Here's the series of problems...

At first, sporadic idling along with random stalls. The stalls are usually at idle or part throttle and are instant, no warning, no flutter, it was just like I flicked the switch to 'off'. The stalls occurred weather the saw was sitting right side up, on its clutch or starter side. Adjusting the 'L' screw was like trying to thread a 5/8" rope through a fish hook. A very small adjustment (1/32nd turn) either way and she would stall out. So I took the carb off, cleaned it out. Replaced carb, 'L' was easier to adjust, may have gotten 1/8th turn either way out of it before stalling. Talked to my buddy at the dealer, he said try and soak it overnight, remove all jets and adjustment needles. Put a new fuel and pickup in as well. After that, the 'L' was better, but still not right. Saw still randomly stalled out, not quite as much. So next thing I did was installed a new carb kit. The 'L' screw is normal compared to my other saws. It idles 'OK', still not right, a little rough. Only stalling out when the starter side is up, even with full tank of gas. (I've been thinking seals in the back of my mind since day one, but it was too random to be the culprit, or so I thought). When it stalls out it just quits, no increase or decrease in engine speed.

I guess I should just have my dealer do a vacuum/pressure test and see where it goes. Would the impulse line be causing this? It just seems odd because with a crank seal going bad, I read on here that the engine will usually race once on its side. Could this have something to do with the coil, as it almost seems to be an ignition issue. This is the first saw I've dug into so I really am having a hard time on where to start.

Sorry for the book, but I wanted to be very clear on whats going on. Thanks for all your help in advance!

Evan

Check your on/off wires from the switch all the way to the coil. If you find a bare spot anywhere on the wires you may solve the problem. From what you describe the saw seems to be shorting out. You gotta decide whether the saw is breaking down or stalling. A saw breaking down ususally takes a few seconds of acting like the switch is being turned off and off before it quits. A stall is more like a saw running out of fuel, a smooth coast to nothing..

 

[Evanrude]

I did check the wiring under the filter base, looks good there. I'll have to trace back to the coil from there.

 

[Martinm210]

I think I've heard on a few cylinders (maybe it was the 066) that there was a large lip on the transfer ports that was causing saws to die suddenly at idle. Apparently this lip can collect pools of gas and suddenly release causing the saw to die. Stihl was having the dealers take a grinder and smooth out these little rough edges.

Ever since I heard about that, I've noticed these on two of my Stihl cylinders. One was my 044 OEM cylinder, but it was beyond repair. The second was my 066 cylider I'm working on right now. I just use a dremel tool and a small sanding/cutoff disc and trimmed off that burr.

Not sure that's the cause of the problems noted in this thread, but I thought I'd toss it out there for something to look for if you pull it apart.

I've been pretty lucking on the carbs so far, just installed new carb kits and both of my rebuilds have had good working carbs after that.

The other thing I've heard is that the carbs have internal check valves that can get damaged from things like carb cleaner or compressed air. If they go bad, the only fix is to replace the carb...not sure there is a way to check those or not though..

 

[Evanrude]

I did fail to mention in my OP that I did try a different carb, not the one on my good running 440 tho. Still stalled on its side.

 

[Martinm210]

I did fail to mention in my OP that I did try a different carb, not the one on my good running 440 tho. Still stalled on its side.

How about the fuel filter or tank vent, have you checked those. When you open the gas tank is there any air movement in/out? Have you cleaned/blown out the fuel filter and tube out?

I wouldn't think it's the ignition. It's a fixed thing, so if it's going to be a problem it would be very consistently that same problem, not sporadic.

 

[Evanrude]

Put in new fuel line. Haven't replaced vent yet. When I open the tank, I sometimes get the 'poof' of air coming out, never a sucking in. Gotta go to the dealer on wednesday, ill pick up new vent and fuel filter for it.

 

[THALL10326]

Put in new fuel line. Haven't replaced vent yet. When I open the tank, I sometimes get the 'poof' of air coming out, never a sucking in. Gotta go to the dealer on wednesday, ill pick up new vent and fuel filter for it.

That poof of air when you open the cap means your vent is probably working. Its a one way vent. Air goes in but no gas goes out. Builds pressure in the tank for good fuel supply..

 

[RiverRat2]

Evan,,

Remove starter cover and pto cover,,,, see if you have any radial deflection of the crank shaft by trying to pry the flywheel or the PTO side,,, you should not be able to move it up or down,,,, if you can see it move,, you probly have worn bearings and seals,,, go ahead an pressure /vac test is next,,,

One of the first 066's I modded acted just like that when you layed it on its side in the cut,,,

ended up needing bearings and seals,,,,,

Good luck

 

[Evanrude]

:bang::bang::bang:

Looking the saw over in the garage for the past hour or so. Checked the 'pry' method suggested by RR2, no movement there. While doing that, I had the starter covers off both my 440's to compare wiring and air gap with thickness gauges. I caught myself turning over the flywheel by hand on the problem saw while reading my service manual. I looked up and the spark plug was IN! So I did compression test, 3 pulls 134psi, 6 pulls 145, it hit 155 at 9 pulls. Then, I took off the muffler and looked at a pretty sad sight.

CLICK HERE FOR FULL SIZE PIC

I've did a compression test very early in the troubleshooting stage, somewhere back in Nov/Dec, it would pull about 150psi in 3 pulls. So, I must have a seal going bad.

Ok, you can all since I didnt do a comp test prior to posting this earlier.

 

[omoranchman]

This is way off the wall but it's happen to me. Check out the muffler. If a piece of baffle is broken loose it can fly around in there and close the exhaust randomly. As soon as the saw stops the pressure is removed, the piece drops to the bottom and all is well until next time. Run it without the muffler and see what happens. Good luck.

 

[Martinm210]

:bang::bang::bang:

Looking the saw over in the garage for the past hour or so. Checked the 'pry' method suggested by RR2, no movement there. While doing that, I had the starter covers off both my 440's to compare wiring and air gap with thickness gauges. I caught myself turning over the flywheel by hand on the problem saw while reading my service manual. I looked up and the spark plug was IN! So I did compression test, 3 pulls 134psi, 6 pulls 145, it hit 155 at 9 pulls. Then, I took off the muffler and looked at a pretty sad sight.

CLICK HERE FOR FULL SIZE PIC

I've did a compression test very early in the troubleshooting stage, somewhere back in Nov/Dec, it would pull about 150psi in 3 pulls. So, I must have a seal going bad.

Ok, you can all since I didnt do a comp test prior to posting this earlier.

Sorry to see that, but it appears it's time for a tear down. Looks like the piston and rings at least need a replacement. You never know on the cylinder until you've got it apart and try cleaning up any aluminum transfer that may or may not be stuck on there.

 

[A. Stanton]

Mine just started to do almost the same thing. I readjusted the slow idle and that didn't help; put a new plug in: problem fixed.