Ok. I put it back together and fired her up. It would idle at about 2600 rpm for a couple seconds then jump up to 3200-3500 rpm for a couple seconds then die back down. Everytime it would idle up it kept going a little higher. It finally idled up to about 4000 rpm then died and would not restart. Came back in and checked compression and it is still at 150. Not sure if it matters but I didn't have a new spark plug so I put an old one in that I had laying around. I'm going to go get a new one in a few minutes and see if that has an effect. Any other recommendations?
MS440 rebuild now low compression
- Thread starter hawk910
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Beer Gut
A Fine Pilsner
Tank vent, air leak some where, bad low end tune are places to look
How long has the carb been out of comission? Metering diaphragm going stiff?
cuinrearview
Red saw lover
My same thoughts. Takes so little to make a carb the issue.
About a year.
I'm about ready to throw this thing against the wall. My local parts store didn't have a plug for it so I robbed one out of a 461. It cranked and ran for a very short time and then died and would not restart. I think the L setting is too rich and I am fouling plugs. Well, I went to the next closest parts store (30 minutes away) and got a couple of plugs. The saw set for about 4 hrs. I put a new plug in it and it still wouldn't start. I checked the compression and it is now only 120 (was 150). I took the muffler off to look at the piston and cylinder and the inside of muffler and the piston are noticeably wet with gas.
Beer Gut
A Fine Pilsner
It sounds like you are flooding then starving after it gets going. Which can be issues I stated above. Clean your tank vent. Blow out fuel filter. Reset your carb screws since way early on you said you adjusted. Air it out, pull plug, BDC dump excess gas out plug hole, dry and heat the plug. Try it. If still racing up and dieing it's a carb issue or air leak.
Time for a full carb rebuild, all new kit, proper cleaning and adjustments/settings. Carbs are very finnicky to have them run right.
Thanks for the advice guys and thanks for being patient. I’m fairly new to chainsaw motors (if you couldn’t tell). I blew the cylinder out to dry it out, closed the idle screw a little and set the L adjuster at one turn out. Installed new plug and she fired right up. I ran it for about 30 seconds and shut it off. I wanted to be able to sleep tonight so I figured I would leave it alone while I’ve got it running and work on it more tomorrow.
Beer Gut
A Fine Pilsner
No have fun. It will come around. If your limit caps are intact you went to far. Follow direction sticker right by screws on cover. Trying to help you eliminate everything as is. If that don't work carb kit. Relax. Saw ain't junk, and your last low comp test was probably because it was so wet.
Thanks. I have removed the limiter caps on the carb.
Beer Gut
A Fine Pilsner
Buy the kit.
Just a little info for the OP on carbs. If the metering diaphragm becomes stiff it cannot flex quickly enough to bring fuel in when required, saw runs lean and fast( revs high). Also the stiff diaphragm will hold the needle slightly off its seat and cause the engine to flood during start up and in many cases will allow fuel to seep into the cylinder when the engine is not running. Your saw seems to be exhibiting these symptoms so the suggestion to do the carb up right seems reasonable. Chainsaw repair is a good bit of fun but it often means many areas have to work together to get one to run correctly, compression, fuel delivery and spark on time will all be requirements for a good running saw. Don`t loose patience and expect a saw that has been apart and laid up to be a runner just by bolting it back together, happens sometimes but in general more often than not a complete overhaul may be needed to get it running properly again. Treat it as a learning experience, have fun with it....
Latest update: Went to dealer and picked up a carb rebuild kit....It was the wrong kit. Got the correct one and installed it. This seemed to help, but the saw was still running very inconsistent. It would run good for 60-90 seconds and then it would die. Couldn't get it to idle very consistently either. I decided to do a pressure/vac test one more time and when I took the carb off I noticed that no gas squirted out of the fuel line. I decided to change out the fuel line and filter with the OEM one. That was the problem. After retuning the carb the saw runs like a top. Only one problem sill remains...it idles fine while holding it parallel to the ground, but if I tilt the bar toward the ground it dies. Any suggestions on what that might be? Also I have learned a big lesson during this rebuild. Aftermarket parts are a big gamble. If I would have ordered all OEM from the beginning I would have saved myself a lot of headache.
Maybe the line had a kink in it? It passes pres and vac you say? Is the carb OEM?
It sorta passed a pressure test. Pressure leaked down very very slowly but it appeared to be coming from the compression valve hole. I didn’t have a compression washer to completely seal it off while performing the test. I don’t think the carb is oem. It does not have “Stihl” anywhere on it.
Conquistador3
Le Comte de Frou Frou
Maybe US models were different, but the MS440 we have here all came with Walbro HD carburetors... genuine ones are usually stamped "Walbro" on the pump diaphragm cover.
This one doesn't have anything stamped on it. I have 3 other carbs off of 460 and 461 and they all have "Stihl" marked on them and "Walbro" on the bottom. I might try one of them. Does the dying when tipped forward issue sound like a carb issue?
Well I say test test and retest until it is perfect then take it from there. Until you seal that leak you don't know if there is another.
