Power Piston in a marine carb

[FGS]

I have 2 SBC engines in a 28 ft boat.  I am thinking of eliminating the power piston in the 2 quadrajets.  I constantly worry that the power piston could be causing a lean condition when I am cruising below the normal cruise rpm of 3k.   I have taken vacuum readings under power and compared them to the different spring rates for the power piston and the only spring that begins to richen the mixture in the off cruise rpm of 1.8 to 2k is the strongest spring.
A marine engine is not like an engine on the road in a car, it's always under load comparable to a truck constantly going up hill, no such thing as coasting in a boat.  So, given this fact why do you need the benefit of a power piston when you are not on and off the throttle for normal driving and passing?  In a boat you normally increase rpm gradually and stay a given rpm for extended periods.
I have done the math and determined that going from a #70 jet to a #64 jet would give me the same effective jet area as I would have with a with a power piston rod in place in fully retracted position.
Any one have experience removing the power piston in a marine carb?  What are the upsides and downsides to doing this?

[Cliff Ruggles]

You don't have to worry about using the Power Piston in a Marine carburetor.   These aren't "fixed" systems and the carburetor will add fuel with increased throttle angle and pressure differential above and below the throttle plates well before the power piston moves up to increase metering area.

So under load the fuel delivery rate increases proportionally.  The power piston will cut-in at some point which occurs under heavy load to increase the metering area.  This happens at heavy and wide open throttle openings when vacuum falls below the cut-in point of the PP spring.

Marine carburetors typically use pretty "soft" springs in them to help with fuel consumption under light engine loads but I've never seen a scenario where they ran the engines so lean as to cause running issues or engine damage.  If you aren't experiencing "surging", power going "flat", detonation, running hot or any other issues then having the power pistons operational aren't an issue. 

The way Marine carburetors are set up you'd need to back the jets off more than .064" when eliminating the metering rods.  It would be trial and error but the carbs will actually work fine without a power piston in them.  I've done this many times to "save the day" with the later CCC carburetors when there was just too much going on with the ECM and related components to get things to work well.

I also run many of our "race" and "max effort" street/strip Q-jets straight off the jets and they are flawless even for street driving.

I rebuild a LOT of Marine Q-jets here and the biggest problems I see with them is folks using kits that don't have the "high flow" N/S assemblies in them and the correct Marine accl pumps.  They pumps being supplied (except for mine) have the soft blue seals on them that don't last anyhow and many are the longer automotive pumps.  I also see a lot of brass floats being installed which is BIG mistake for them.  They do not have the buoyancy to put adequate leverage on the fuel inlet needle to effectively control the fuel level when using the high flow N/S assemblies.

I'd like to have a nickel for every complaint I've had from folks who just "rebuilt" their Marine Q-jet with the wrong parts, or had it done someplace and are having issues with them simply because they used "generic" instead of the correct Marine components in them......

[FGS]

Thanks Cliff for the info on power pistons.  After reading your response I went back and read up on Jets and Rods from your book and other sources that I found.  I have come to the conclusion that my fears of a lean condition on part throttle from a too weak power piston spring are probably over thinking the subject.
As a result I’m going with the stock spring in the carb and 70 jets with a 42 rod.  This may be an over rich setting so I’m going to set up 2 spare carbs with 69 jets and 39 rods.  After I get back in the water this spring I will evaluate the 2 different jet/rod combos.
I still think the need for the power piston in a marine application is not required but I just don’t want to spend my time on the water chasing the right primary jet size.