John B

So,
Everyone seems to agree, you must find out what the vacuum is under the carb and under the blower, it will be different. What are the values just above high cruise speeds? What power valves (opening values) are available. You will have lower vacuum under the blower vs under the carb. If you have 0 vacuum under the blower and 5 in. under the carb were you want to go rich --- what power valve do you want and were can you hook it up. I don't think they make power valves under 2 in. or so! Big heavy boats are under boost while cruising, small boats aren't.

There is still no substitute for carefull testing and understanding what is happening.

I wonder about only boost referencing half of the carb, sounds like a good way to maybe burn down only half the engine

Single carbs (1050's+) on B&M 250's should be run sideways, because at all but full throttle--- all the fuel is directed to the center of the carb by the throttle plates. In the (primarys front) location most of the fuel goes to the center cylinders and 1,2,7,8 will run up to 250 degrees hotter.

This boat we dynoed and tested on for 8 years, it was a 38 Topgun with crate 502's, 7.5 CR, Merc 800 SC cams, BM 250, 1050 (Nickerson) #92 jets, drilled power valve channel restriction to about .095..4.5 power valves (with below carb reference), 8 psi, Inconal exhaust, 30o timing, CMI elbow tops....
Dynoed 680HP
The big fellow ran 80 and blew TRS drives all over the place. So I bought a Skater!

Most of this work was done in 1995 and the motors haven't been out since.

This isn't grapes, I hope it can help you guys have great boating experiences, not problems. JB

blown1500

Sorry , Guys,
The power valve we start with is the 2.5, not the 4.5 I said above. You may end up with a 4.5 or some other number, but we always start with a 2.5. SORRY!!