Having problems getting my old Stihl 048 to start after sitting for a few years. There is way too much compression, I can get it to turn but it's extremely difficult and it will not come close to firing. With the plug out it's as smooth as butter, so don't think it's a starter rope issue or lack of lubrication in the cylinder.

Have peeked in the cylinder, was a bit of carbon build up on the piston which I've cleared out with carb spray and compressed air, looks better now, but made no difference to the extreme compression. Plug has been cleaned thoroughly. Took the muffler off, exhaust port looks fine, no blockages.   

Is there anything else worth trying?

Thanks