I have a briggs stratton 16.5 model 313707 when I try to start this, it won't spin the flywheel. But if I take out the spark plug it will spin just fine. What is this problem.

Sounds like you need to have your valve clearance checked.
Luck

Checking the valves is most likely the best place to start. How long as this engine been sitting without running? Have you checked the oil, was it unexpectedly over filled?

Just for the winter storage

What is the valve clearance for this model

What is the valve clearance for this 313707 model type 0126-e1.

Check the oil first. Was there gas in the tank over winter?

Are you sure about your model number? Small Engine Manuals | Lawn Mower Manuals | Briggs & Stratton (http://www.briggsandstratton.com/support/operators-manuals/?NTT=313707) This is the engine number and not the tractor model, right?

Rotate engine 1/4 inch past top dead center and set valves at .004 both.
Luck