Takes a while to start after sitting a few days.

I'm using the manual fuel pump. G63b 2.0 motor. It took several minutes before it started today. It had been sitting for more than 7 days. I pumped the gas while cranking and then held it down. Neither seemed to help, I just got dry cranking. It took a while for gas to get back up to the carb. I'm guessing it evaporated or drained back to the tank. But I would have thought having the regulator on it would trap some gas in front of it that would let it start and get going.

Is there anything I can do without having to add the electric pump?

What's the weather been like? Weird question but if you've had a couple of cold starts the air in the fuel tank can contract and make sort of a vacuum in the tank. Next time try opening the gas cap before starting it and see if it makes a difference to how long it takes to prime the carb.

I have that problem with Geronimo - the weber carb I have on him has an open bowl vent to atmosphere - the gas evaporates out of the carb. I will be changing the head gasket and putting on a modded head and I have a 38 dges carb with a closed vent bowl that I will tie into the evap recovery system to reduce the loss of fuel.

You can also try a one way valve between the inlet to the carb. and fuel pump.

A check valve would help, but be sure it is a 1/2 to 1 psi spring loaded check valve to minimize the pressure drop to the carb when running. A lift check valve is too hard to use in this application, as it requires perfect horizontal alignment to work properly.

Weather has been warm to hot going into the 50'sF overnight. I'll look for the check valve