Stihl MS 250 VERY hard to pull through

[catch]

My Stihl MS 250 is suddenly very hard to pull through when attempting to start. When the plug is removed, it pulls very easily and it had good compression. The pull rope seems OK and it pulls normally until the plug is back in. I have made sure it is clean and lubed. The plug is correct. I don't know what is holding it back. It is so hard to pull that I can only get it through 2 compression strokes if I pull it very hard. Hope one of you good folks can help......

 

[Nutball]

It could be a thick 2 stroke oil in combination with cold weather. I've had some of my saws get stiff in the winter using Red Armor oil. After a few pulls it usually loosens up. I have found in my experience with a ms250 that they already have very good compression, and are not the smoothest to pull over.

Is it any easier to pull with the switch in the off position? This can help rule out ignition timing problems.