Small Engines (Lawn Mowers, etc.): Mini-Bike Lacking Power, engine model type, shop teacher

Question
I recently started to take apart a 3.5 HP B&S engine from a mini-bike.  I only got so far as to take the flywheel off, unbolt the crankcase cover (under the clutch, it never came off), and take the head off.  After I put it back together, the engine will turn the back tire, but there is barely enough  power to move the weight of the bike itself while sitting on the ground.  Both my shop teacher and I are stumped at this problem, especially since I hardly took anything apart.

Answer
What is the engine model, type and code number?  Are there points in the engine?

Did the clutch sustain damage when removed and re-installed?
How easy does the rear wheel turn by hand?
Will the engine accelerate to full speed with and with out the clutch removed?
Let me know.
Eric