David,


The average crankcase pressure varies from a negative value at low throttle openings, to a positive value of about 5 psi at maximum power.

An R/C carburettor, even in a boat, will not properly cope with such changes.

An engine running at constant full throttle, like F2D C/L speed, or F3D pylon racing (I don't know the boat racing class...) will do much better.


For an R/C engine, just use muffler pressure.