Float bowl level drops overnight

[Remedy]

Hi all... I need some help with my 3g. I didn't luck out and have an Accord given to me, its a Civic instead (1987 California Automatic).
Its been a long road getting this thing running, but Im nearly there.
I had a lean idle mixture that made the engine miss, so I rebuilt the carb in desperation. Now the mix is rich enough but there is another problem that I never checked out before the rebuild. Every morning the car starts right up and then dies within a few seconds, after a few cranks it starts right back up again and runs. I have noticed that in the morning the float bowl level is below the glass. Once the car is running the level goes to the upper mark, I set it there because I was stalling on corners when I had it at the lower mark.
While I was looking at my carb during a warm up, I noticed that my primary booster venturi is dumping a steady stream of fuel into the throttle body, but when the fast idle kicked off it stopped doing it. Is that normal?
Any idea what is happening to the level in my carb?
The final job on this car is going to be finding the reason why it never gets over 26 mpg, I hoped it would end with the carb overhaul.
I really need advice, carb knowledge seems to be mostly in the motorcycle world and those are just really different.

[russiankid]

When my fuel vent valve went bad, i would get around 20mpg and crappy start ups in the morning. What would happen is the valve would not hold vacuum when the engine was off, so fuel would evaporate from the fuel bowl. The valve is there to prevent fuel evaporation. My guess would be to see if you have that valve, and see if it holds vacuum.

[Remedy]

I have one of those, thats the one that lets the vapors from the charcoal canister get sucked back to the carb right? I dont know about the valve, but the diaphragm has a tiny leak. I thought about replacing until I saw the price at the dealer (no one else has those). If that took care of it for you, then I guess its worth the $60.