I run Bob Madara's cams that are ~228 I, 232 E duration with ~.598 lift on both I & E, pretty mild idle but they pack the charge in really well on the top end. Peak hp is at 5500 rpm. I am still in the 90-91 mph range but looking to do another project with Bob this year to take it up another notch.

You spinning 30s at 5500 with nose cones right.

yep.

Try cleaning the air bleeds with some carb. cleaner, by sticking the red nozzle into the air bleeds. This carb. worked well once upon a time. Also a blown power vale will cause ir to be rich at idle.

I would first warm engine to operating temp set floats, and then set timing. I would run as much intial timing as possible at least 14 degrees with full advance around 35 to 36. Then set idel mixtures to max vac or rpm usually 3/4 turn out. should idel about 950 out of gear. put boat in water and install vac gauge. make sure when ideling in gear u do not drop vac under your power valve vac rating which is usually a 6.5 vac rating. If you are below that you need to change powervalve to lower vac opening then in gear idel vac. Just my 2 cents good luck!

That how we do them, Great advise... Pete

Just a thought but my carbs were set up by Dean at Nickerson's and have always worked perfectly till I got my first tank of fuel with alcohol then they idled just as you stated all the carbs needed a extra 1/4 turn at each corner in the idle circuit. then they were back to there normal idle