I was having some issues with my 98 kitty cat...It seems run excellent on a stand at full throttle then bog out.

I thought it was a gas and carb issue and after fully cleaning the factory carb 3-4 times and screwing around with the governor i bought a 18 mm mikuni carb from Laager.

It seems to still be doing the same thing... bogs until you lift the rear end and give it full throttle.

It seems like theres always air in the fuel line too..since the bottom of the petcock is bearly higher then the top of the fuel line input on the carb.

Any suggestions?

Replace the spark plug. 99.9% sure this is your problem.

I had bogging issues with my daughters 77 kitty. It turned out to be incorrect float height in the stock carb which I only found out when I replaced the float with a new one. The old float was fine, just not set at the same level as the new one. I also replaced the needle/seat and carb gasket while I was in there. Obviously this is not your case due to the fact your getting the same results with a new carb. It is a new carb, not a used one, correct?

Start with a fresh plug like dunno513 said, then let us know how it reacts to that.