Need some help with a MS280

scut207

scut207

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So to preface, I am no small motor guru. My father was, owned and restored some 300 antique chainsaws (if anyone is interested in those please PM me some are really nice 40s through 80s gear fully restored) as a hobby, but he passed away. I went through an picked out 2 of the newer looking saws from the massive collection a MS 280 for light duty stuff and 440 in case I ran into anything big, I also have a 34AV. The 440 runs like a song and the MS290 did up until I tried to tackle a a good 24" maple tree from a micro burst.
After a bit of going at it, I first noticed that it would die when no throttle was applied. The carb style has L H and LA adjusters... I tried adjusting the LA and couldnt get it to keep running. So then I started farking around a bit and now cant get it to run on anything but a partial choke or too high idle and when I gas it it bogs and if I can get it past the bog it gets going it sounds real lean...
1) It seems to have good compression without choke on I can hang in in the air by the pull cord and it takes some good shakes to have it cycle.
2) I pulled the muffler and the piston looks spanking new. no scoring at all I was very worried about this part because of it sounding pretty lean for a couple moments before I shelved it and got the 440 out to finish the job even though its heavier, theres little or no carbon on the spark mesh.
3) when I uncap the gas after pulling my ass off on it is seems to escape a lot of air not suck in, I did notice that the breather cap that looks like a distributor looking thing on the gas tank looked plugged, so I popped it and cleaned it out with a dental pick, but no change.
4) The carb adjusters for H and L still have have the safety plastic plugs in there that prevent you from changing it too much. I may have over torqued on out of ignorance, but I don't believe that should have anything to do with jsut a low idle.
5) I can get it to run and idle high off choke where the chain is running at a faster than would like speed but as soon as I richen up the mix to slow it down it stalls, and If I try to get it going it bogs, I have to feather the hell out of the throttle and sometimes I can get it to go but it sounds lean and I am nervous about keep trying.
6) I did disassemble the carb (mostly) I only took off one cover the passive side with only the little screen where there were no moving parts and I blew it all out with wd-40 and let it air dry was supurbly clean.
7) I tried running without the air filter just to see if that was the problem and it didnt change anything

At one point I did have to yank on it pretty hard because it got pinched. The tree was under a lot of tension due to the massive crown and it broke a good 5ft up. I am wondering if I ripped the rubber boot /manifold that goes between the carb and the cylinder head. but I didnt tear down far enough to inspect as it looked a lot more aggressive of an undertaking.
What would some of the vets do first next? I used to just call the old man and he would help me, but the resource is gone. I have zero chainsaw specific dignostic equiment, I have basic standard and metric tool sets , sockets / wrenches allan sets,, and the correct star point screws to rip it appart ,but cant do an actual compression test. I am mechanically pretty rank amateur beyond the above diagnostics.
I also run on ethanol free gas with a very rough 45sh:1 mix... I use the little squeeze top style 2 stroke oil. pour it into a gallon can and then add gas and shake it pretty good. Its not an exact art. and I was unsure if I should be running 50 to 1 or 40 to 1 so I split the difference, fuel is brand new.
 
ZeroJunk

ZeroJunk

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On some of those saws when you really yank on it you can pull the impulse line off of the carburetor housing.
If you take the covers off you may be able to take a flash light and see if either the intake boot or the impulse line has pulled loose.
 
scut207

scut207

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Jun 25, 2021
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Thanks guys! I think since the disassembly goes all the way to the manifold boot I'll hope to find the issue with visual inspection. if not, I dont have access to a vacuum pressure pump atm the only local to me that sells one is junkfrieght


would this work?

In one part of the video he showed testing the gas filter at 3:15sh , saying some have a valve do stihls do this? said it should hold some pressure/vacuum but wasnt specific to which or the amount... any rough idea there?
 
irhunter

irhunter

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Thanks guys! I think since the disassembly goes all the way to the manifold boot I'll hope to find the issue with visual inspection. if not, I dont have access to a vacuum pressure pump atm the only local to me that sells one is junkfrieght


would this work?

In one part of the video he showed testing the gas filter at 3:15sh , saying some have a valve do stihls do this? said it should hold some pressure/vacuum but wasnt specific to which or the amount... any rough idea there?
AFAIK, there is no valve in your fuel filter.

$65 seems like way too much for a HFT tester. I would start by asking around among your friends...people who work on their own cars often have the pumps and gauges you need. Or, maybe an auto parts store has a loaner set.

If you must buy one, I would consider this:


You may need to fab up some adapters and an exhaust port plate.

Roy
 
RED-85-Z51

RED-85-Z51

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Most likely tore the boot, i got a nice 280 cheap because the guy yanked on it and ripped the boot and it did what yours us doing

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