I have a 750 Holley Carb that has developed a leak in the base of the carb. Didn't know it until I had trouble getting the car to run and picked it up off of the manifold and gas was running out of the small hole beside the base screw. The hole goes into the body of the carb from the base up into the cavity behind the power valve. Have changed power valve gaskets and it still gets fuel trough and runs out the bottom of the base. Any ideas how this happens and how to repair it?

Picture might help

Change the power valve itself.

Have you tried a new baseplate gasket?

Sometimes a stopped up air bleed can cause leaks and drips. But, that said, never saw it cause one at the baseplate. I would dissamble the carb and clean all the passages. Check the base and main body for square. Put back together with a fresh base to main body gasket.

Sorry could not be more help. But, I am not sure without seeing the carb where your leak is or where it is coming from.

Leon

Level of certainty that's the source? Liquids (fuel, oil) are funny sometimes and will run along surfaces taking the fluid away from where it's actually leaking from.

If not absolutely certain, may be worth a few minutes of studying the leak a bit.

Look real closely at the pump squirter circuit, make sure the gasket and or metering plate isn't allowing fuel into the back of the metering block. Ckeck the simple stuff first, power vale and gasket, warped metering block and so on Lots of challenges(Murphy Law ) out thier waiting to test are trouble shooting skills