Did you always use the correct fuel mix??
When the rope is yanked from your hand, it's usually timing. But being hard to pull sounds like light seizure problem. The timing is fixed on these saws, but a seizure or sudden stop can cause the crank/flywheel key to shear. This will change the timing and cause the ~SNAP~ problem. It's simple to check if you want to give it a try.

cloudcrasher,thank's for your sugestion, I was thinking if the fly-wheel key was bent the saw would do it all the time or not start at all,the next thing I'am going to try is higher octane fuel maybe my 87 octane isn't 87 or the Ethenol blend is causeing pre ignition?

It would do it all the time, and if it did start, it would POP and run really rough. Here's a few simple things you could try, if you have the tools. Remove the recoil cover, and the flywheel nut and washer. You don't need to remove the flywheel to see if it spun on the crank. You can see the cutaway for the key on both the crank and flywheel just by removing the nut and washer. If they are still in line,that's not the problem. Also,remove the muffler, looking through the exhaust port, you can see if the piston is scored while rotating the flywheel. The 87 is not the problem....unless the mix is wrong.

If choke closed open it small amount to let some air in rope should pull easier after pulling crankrope twice you should open choke pull once so air can enter. If place where bought saw has good saw mechanic they should fix saw by grinding off choke plate so air can enter a long with fuel. My o38 stihl pull off your dayem fingers if don't let in some air.

Thank's to all who responded today I went to adiffrent Sthil dealer he sugested a new spark plug and said the model MS250 is prone to hard pulling, changed the plug and noted the new plug has an R in the number gave it a try and it started up on first pull! I think the R in the plug number means it is a resistor type may be that retards the spark a little? thanks Paul

1

I was wondering if carbon build on piston causes too much compression?

Excessive carbon on the Piston Crown will definitely increase compression . It will also cause ring fouling and hot spots within the combustion chamber . Decarbonizing use to be routine , use premium syn oil and run 50:1 no more or less . Also ensure fuel is fresh , within 60 days old with The E fuel usage !

Same problem

I ran the chain around by hand and felt it loosen up

Tried it and it was way easier to pull

Something in the chain drive?

Has anyone determined why the MS 250 chainsaw becomes hard to pull? If I remove the sparkplug, it pulls easy. Started becoming hard to pull when cold but normal when hot. I had it serviced but still a problem. Now hard to pull when cold or hot. And I just broke the cord trying to start it. Is there a solution to this issue

C

Just broke my cord trying to start my MS250 also. Have no idea why it is so hard to pull. Once it starts, it runs fine.

The jerk back or pull back is because the flywheel is moving (migrating cw on crank snout), only a few thousands of inch, this is probably from over revving. The snout of the crank where the flywheel is mounted has a key way, the newer flywheels do not have a key or key way , they have an integral aluminum key built in to the flywheel, this is advancing the timing causing the pull back reverse rotation. The fix is a new flywheel & Lock-Tight, no more free revving.

The ms250 has always had ths issue poor design . You must ensure you torgue the fly wheel exactly .

Ok, I'm guessing there's general categories of why a pull cord has a lot of resistance..

Mine is due to some serious pressure in the chamber..

I removed the spark plug and it pulls like a breeze..

I turn-in the spark plug loosely (one or two threads) and I can pull one (maybe 2) compression stroke(s), then continue to the next stroke after the pressure releases through the plug/thread gap (I can literally hear is hissing out since I have the sparkplug loosely fitted)..

So then I return the sparkplug normally and pull the cord until the extreme resistance is at its peak, hold the cord in position, remove the plug and see the piston is just before TDC (top dead center). And (still having left the cord in the same position) if I continue to pull after removing the spark the motor turns very easily (normally) as usual with the plug removed.

I feel like there's an unusually high compression in the cylinder.. possibly as a result of the pressure from the previous compression stroke not being fully released..

So I pull the valve cover and check the exhaust valve from the valve pusher (sorry my engine vocab is a little crappy).. the valve rod/pusher moves up and down appropriately so I assume the exhaust valve is opening.. (I don't want to remove the head to verify, because I can't imagine the valve actually stuck to the valve opening and the valve rod just freely moving/broken)

All I can tell fairly certain is that the resistance is due to cylinder pressure, but don't understand how that much pressure can build up? Wouldn't the pressure at least be release back into the intake when the intake valve opens? Or should there be suction at that point if everything is working as normal?

I think I noticed something about exhaust blockage? Is that a thing? Common?

Are there some pressure readings I could verify? (not that I have the tool for that, nor do I want to buy it!)

Anyway, thanks for the help and I hope the info on my situation is clearly presented.

Cheers,

Tony!

Tony

2 cycles do not have valves. You have posted a good story but have ABSOLUTELY no idea what you are talking about.

Actually , there are a few 4 stroke chainsaws that are available however yes this thread is entitled " Stihl MS-250 " a two stroke engine design !

I have never seen a 4 stroke saw.

Only a few manufacturers , Google it !