Disassemble the starter and look for broken parts, any parts that look like they have been binding.
Hard to near impossible starting due to too much compression sounds like a fuel issue where fuel is bleeding into the engine when the saw is not being used and this fuel eventually evaporates, leaving the residue oil soaked in the crankcase and when you try to start it again after it’s been stored for a while, that residue oil is picked up by the new fuel entering the crankcase and then pulled into the combustion chamber and settles around the compression rings and on top of the piston and this is why it feels like it has 300 psi when trying to pull start it, because instead of having a 50:1 fuel mix, with each pull of the starter cord, more oil is sucked from the crankcase into the combustion chamber so that it has now become a 5:1 fuel mix making it near impossible to pull the starter cord. The cause of this issue is one of two things. My guess in your situation is that it is a blocked fuel tank vent valve which is causing the fuel tank to build up excess pressure when left unused or it could also be the needle and seat not seating properly anymore and allowing fuel to bleed down in to the engine when not being used. An easy test once you do get it going and burn & blow out all the excess oil (I usually flush them with about a tablespoon of straight petrol by pouring petrol down the spark plug hole, turn it upside down and vigorously pull the starter cord to clear the oil and fuel), is to drain the fuel tank completely and then run the motor and again until the motor complete runs out of fuel that is still in the carb and fuel line. Leave it sit for a few days with the fuel cap loose and then fill it with fuel again and it should fire up without an issue or alternatively store the saw on it’s side with the fuel cap left loose. I would be replacing the fuel tank vent if it now starts easily and runs like it should after doing this test. About a 10 minute job and the part is dirt cheap. Photo attached of my MS310 which may be slightly different to your vent valve setup, but it will be basically the same set up. The later MS311/391 had the vent directly installed into the top of the fuel tank and they are a real pain to replace. Why they decided to make it hard to replace on the newer models, I have no idea as this part (fuel tank vent) is something that regularly fails as the saw gets older and on the MS311/391 the vent is now in a spot where it get absolutely filthy from oil and dust. Cheers
You could be right, but I am more inclined to think that when he is turning it by hand is that it is slow enough to release the extra pressure in the combustion chamber, where as when he uses the pull start the flywheel is instantly spun and can't release the pressure quick enough and jams until it release enough pressure to continue turning a bit more. Usually if you leave it sit for 30 seconds you can pull again with the first pull relatively easy and by the 3rd pull its jamming up again because it has sucked in more residue oil. I have fixed heaps of these with exactly the same issue, but I am not saying you theory is wrong either because like you I can't physically see the saw and test what it's actually doing, so YES it could be the cord as you suggested jamming up, but when you think about it, what would it jam on. I can't think of anything. Cheers
He states that he removed the pull starter and was able to turn the engine by hand, so it would make perfect sense that he would have also checked that the starter pulled out freely while he had it removed from the engine.
Never assume. Daily working in a shop would say no.
Maybe your right, but it seems very pointless checking the engine and then not checking the starter when its off, but as you said, some don't look at the big picture, but I still feel my initial diagnosis of a fuel bleed off into the crankcase and then evaporation of that fuel leaving just the oil when left stored is the real issue and is indeed correct. I have seen this same issue quite a few times and I am sure you have too and this issue it's not restricted to just chainsaws.
Take the plug out and see if it jams!
I had to fix an MS880, when they do not start right away, that saw will make you feel real old very quickly!
I have come across worn starter pulleys, part number 6 in the above diagram.
