Q: These YH's were rebuilt about 6 years ago using Daytona parts rebuild kits and their flat needle and seat design. Had run great after the rebuilds. Then after a fuel pump rebuild this spring, I'm back to the notorious problem of fuel out the aft carb throat. Pressure has not been checked. Float levels check to factory spec 9/16" front and 7/16" rear. Per your YouTube tutorials, blowing into the fuel inlets the needle/seat seem to not leak. Also per your tutorial the metering rods check as well as the accelerator pumps. Hard to tell with these carbs sitting down low in the engine valley but it looks like I'm getting fuel dripping out from the throttle butterfly shafts. Rebuild again?
A: To me, it's suspicious that this started after rebuilding the pump. I would test the pump pressure before going any further. Not sure what the actual spec is for pressure but imagine it isn't more than 4 lbs. You may have to add a regulator.
The other thing that brings up a yellow flag is the fact it's been 6 years. Being a marine carburetor I'm sure it sits around a lot. Your carburetors are probably dirty and that will cause flooding.
The most common problem is dirt, or bad needle & seat.
Test your needle & seat - Did you damage the viton tip when adjusting the float? There may be dirt in the seat. Be sure the gasket is under the seat.
Has your engine been sitting for months? If so then the gas has probably turned and coated the inside of the carburetor. A thorough cleaning is in order.
Test the fuel pump pressure for not more than 4 lbs.
Does the float have fuel in it?
Check float level, but unless it's way off, then not the problem.
Is the float clear on all side and not rubbing.
Move float up and down to make sure it isn't catching.
Is there a return line on the fuel filter? If so make sure it isn't disconnected.
Fuel filters might need to be changed.