You can leave it in, however it adds 4-5 hours of work during the process and you have to have the drive out to align the drive
Just pull the drive since you have to pull the drive every year for PMs. Motor should take less than 45 minutes to pull
Only take 2 oz of water to froth oil
Did you drain the block and manifolds before pulling Anti Freeze in? If you didn't drain, you most likely have a cracked block
Drain the water, pressure test. Should hold 15psi forever
Rain won't get into the motor unless the whole motor was underwater
Is this a salt water boat?
How was the boat winterized?
Most Mercruisers after 2000 have a drain hose connected to the garboard plug.
What sized Holley? 4150 or 4160?
Did you verify the idle transfer slots when you had the carb off
If your fouling plugs, you are too rich
Start at 3/4 turn out at mix screws.
Make sure the float levels are set (external adjustment)
When you had the carb apart, did you make sure the air...
Take your current prop, and do a run, 3-5 miles at WOT, then come back the other way document your RPMs and your speeds.
If you are getting 4600-4800 RPM, the 19 pitch prop is correct
I get better luck with an unlit propane torch by waving it over a carb
If you add a bit of propane at idle and the speed increases, back the idle mix screws 1/8 turn.
If you add propane and the idle drops, you are rich, and need to turn the screws in 1/8 turn