HomeLite UT20042A 2-cyc Trimmer Very Hard to Pull With Plug Inserted

I have a used Homelite UT20042a 2cyc trimmer. I put in a new recoil cord which now works fine and pulls easy (normal I think) when the spark plug is OUT. When the plug is IN it becomes ridiculously hard to pull the cord. I removed muffler and exhaust components, but the cord still pulls (and turns over) extremely hard. This is bad for my shoulder, and I wonder what else might cause this problem that is worth fixing ... before I give up on this trimmer. Thanks !
 

Thanks Roy.  There is no KEY mentioned in the parts diagram for the 20042a, and the entire flywheel costs around $20 used.  I'll see if the flywheel is easy to get off, but considering there might be other problems as well (like I know the fuel line is broken), the repair might not be worth it for this old trimmer.  
 
You got me thinking a bit more.  So when I turn the flywheel by hand, it is easy without the plug. But the 1st cycle is hard WITH the plug in ... the 2nd cycle (exhaust) is easy either way.  There seems to be a LOT of compression when the plug is IN, and that I think is what I'm feeling.  The flywheel and piston do turn smoothly. The exhaust system is still removed.  I wonder if these are usually quite hard to pull when starting ??

 
 
 

Thanks for all for your responses.  I bought this used: pull cord was broken and seller said it ran a couple years ago. I cleaned it up and replaced the cord, and I'm quite sure that was all done correctly (quite a pain).  I recently put a little PB Blaster into the cyclinder, and I think (well I think) it now pulls a little easier (with plug IN).  I also checked that I have a spark (so I don't have to deal with the coil).  But it would not turn over when I sprayed a little starting fluid into the air intake (behind filter) or into the cylinder (and then replaced plug).  Wish I had a compression tester.  I guess I'll go ahead and replace the gas lines and then see if it starts.