The Mikuni is quite a good carb when tuned and you may be confusing some things here. The classical definition of flooding an engine comes from the days of carburetors in cars that had accelerator pumps. If the engine wasn't running and you pumped the throttle too many times the intake manifold was full of fuel often fouling plugs with gas. These carbs don't have accelerator pumps so that can't happen.
The problems commonly ascribed to the Mikuni is a condition where fuel gets splashed up into the vent tubes for the float bowl and then continues to flow because the vent tubes are too long and end below the float bowl causing them to act like siphons. The vent tubes are the two hoses that come out of the sides of the carb. The other hose that comes out of the bottom of the carb is the overflow for the float bowl. If fuel is pouring out of the overflow your float valve is malfunctioning. This could be an assembly issue, floats rubbing on gasket, adjustment way off or a worn /damaged float valve.
First off remove the carb and nip a small hole in both of the vent tubes about halfway up the carb body. This kills the siphon action and any fuel that gets splashed up into the tube will just flow out the tube or flow back into the float bowl. While you have the carb off open the float bowl and make sure the floats are not rubbing on the float bowl gasket. If the show and wear marks trim the gasket with an X-Acto or similar razor knife. Make sure there is no gas in the floats as they can spring leaks and hold the valve open. Check adjustment for float height and travel (that little tab that's bent at a 90 degree angle and hits the tower the float pivot pin goes in). The valve only needs to open a few mm. More than that and you won't get anymore fuel flow but the floats will slam around causing the mixture to be inconsistent over rough terrain. This tab is usually set to allow far too much float travel. Check the Viton tipped needle for debris or damage and same for the brass valve seat. Big advantage of the Mikuni is the replaceable valve assembly. The Keihin is just machined into the body.
All the instructions for soldering tubes and drilling extra vent holes is overkill. Nipping the holes in the tubes works.
As for starting issues that generation of Betas was infamous for the ignition trigger coil going bad. It's easy to think the problem is caused by the dribbly carb but it was often not the root cause.
...and I hate Del'Ortos