This is kind of normal for a carburetor and modern fuels. They evaporate out of the float bowl and the pump takes a minute to bring fresh fuel back up from the tank.
If it was not doing this before, did you change anything under the hood, such as the air filter housing?
If it worked fine before, and you have not made any changes to the setup, then maybe the pump is getting old, the fuel is getting more volatile with a different summer mix (do they make the summer mix more or less volatile?), or maybe they have not changed over in your area but the weather is heating up.
Probably other things can cause it as well, but those seem to be some basics.
Have you owned older carbureted vehicles before this one? How old is the gas? How long has it been since a tune-up? Is the tank at a lower level than before, or about the same?
Good luck.
Paul
