mrgnstrn,
I have had a number of 9.9 Mercs and:
1. I generally have to keep the panel out and the hatch cracked on a small prop for air.
2. You could have bad new plugs
3. bad gas or bad mix
4. Could be crud in the tank even if new
5. The interlock in the remote control might not be indexing in the correct detent to run. These can be a bear, I had problems and it took a while to sort it out. This is the same detent ring int the remote control that prevents you from starting it in gear.
6. Might be a bad carb or mis-adjusted.
7. The first thing that I do with a new tank or hose is to pick my spot and cut the hose in two and install an inline fuel filter.
8. Possibly a bad ignition switch
9. One last one that I also have had problems with is the lanyard switch that in Illinois is supposed to be clipped to the operator when the engine is in gear. Make sure the clip is properly holding the interlock switch in the run position.
Good Luck, Jim