It seems like mopar346's problem has been answered. It's evaporation.

I'd like to add priming SHOULD not be pouring fuel down the venturi. That is a good method of drying off the cylinder walls. Especially when 90% of us will be pouring in way too much. Use a squirt bottle to add 10 or 20 mL into the front bowl. Then you can control the pump shot with the throttle just before you crank.

As for spinning the starter with to build fuel and oil pressure. I'm also guilty of doing this in the past but when you consider oil will not reach the piston rings, wrist pins and walls. Instant fire up is better for engine life.