You definitely need to do some work on your motor, that speed is WAY low, you should be able to hit 20MPH no problem tuned moderately well.
You didn't answer the most important questions, being:
WHAT TYPE OF CARB DO YOU HAVE???
People often say "I have the stock parts from a new kit" and think that conveys all of the info needed, not true, these motor kits are all similar but can be VERY different. Specially the carbs, the CNS is WAY DIFFERENT than the NT or Speed carb.
So please post back exactly what kit you bought, and what carb came with your kit and THEN maybe someone can help you with your problems...
From what you have said I can only make one comment, you said everything is new and stock, so air filter is clean etc. You also said you turned your carb upside down and fuel came out of it (I assume while working on it). These two statements do not jive, cause it is likely when the fuel came out of the carb it clogged up the air filter with oil residue. (unless the filter was pulled first).
At any rate, let us know what carb and kit and we will try and help you.....