Murray 17/42 will not start

I cannot start my lawnmower due to the string being so hard to pull. The engine WILL turn as I pull the string but its just so hard to pull that there is no way that I will get enough force to start it. This happened just randomly last time I was using it. Everything was working just fine when I shut it down to empty the bag, but when I tried to restart it to continue this problem started. To start off I do know the basics of an internal combustion engine. I have checked many of the common problems related to something like this but to no avail. Here is everything I have done: Removed sparkplug and tried cranking it, but still stiff Removed recoil and checked it. Pulls smoothly when not attached to engine Removed blade Removed carburetor and even cylinder head, then tried cranking but still stiff. I admit that I am probably well overdue for an oil change on it but it did have oil when checking everything I just stated. Any suggestions on what else can be causing this problem?

Hi, I have a push lawn mower with a pull start engine, tried to use it after being stored for a month and it was hard to use the pull start. After reading other posts here, I tested with the spark plug removed and it turned over freely so I put the spark plug back in and it fired up right away, I ran it for maybe 15 minutes, there was some initial white smoke from it but nothing else. After leaving it for a few minutes I tried to start it up again and had the same problem with the pull start being hard so it seems as though every time I want to start it I have to remove the plug and pull the starter a couple of times then put the plug back in and it starts again - I can live with this but I'd obviously prefer not to have to do this every time I want to use it. Can anyone offer any assistance as to what I can check next? - I've check oil levels and replaced the spark plug. Thanks