Small Engines (Lawn Mowers, etc.): gokart wont start, compression resistance, starter fluid

Question
hi john i have a 150cc talon dlx 150 iir and it will not start. it has a good strong spark, no water in the gas and i tried starter fluid in the air filter and the plug whole still nothing.      

   thanks--max

Answer
The third variable would be compression.  When you pull the rope, what does it feel like?  Over the winter a valve might have stuck open, and there would be no compression resistance when pulling the rope.

Also, a sheared flywheel key is a possibility, you would have spark at the wrong time.

Give me some backround.  When it last ran, did it quit on you?
Did anything out of the ordinary happen?

Can you find any brand/model numbers off of the engine?