Motor does not spin freely with no plugs in!

[sunbird 18]

I am still working my way through this 94 yamaha 250 carbd txrs that I got. THe powerhead seems excessively noisy to me. With the plugs out, i tried to spin the flywheel by hand. It spins freely for about 1/6th of a turn then there is a very tight spot where I have to back the flywheel up and try to accelerate through it. Kinda like a 4 stroke when trying to rotate through the valve opening. It even springs away from the hard spot once you are "over the hump" There are 6 discrete tight spots in each revolution of the crankshaft, each of which is 1/6th of a revolution apart while turning the flywheel. This seems wrong to me. I cannot think of anything that would cause this?
Is this normal?
Is something definitely wrong with this picture?
Please help!