Danny_Ocean

"Bubba" (affectionate term for the previous owner of my boat) installed an automotive carb (in addition to an auto starter, distributor, alternator & water pump). The carb is a Holley 750cfm "double-pumper" with elec. choke.

I have found, what appears to be, a reliable supplier for remanufactured marine carbs. Based on info provided, supplier suggests swapping current carb to a 650cfm marine carb. Supplier believes the 750cfm is too big for my application.

Boat is a 25' Corsa (4500lbs) with stock 454/330 (mild cam). It seems to run OK with the 750cfm. I'm not a "speed-freak" and am more concerned about gph.

Does this swap sound reasonable?

Many thanks in advance,

D. Ocean
Pompano Beach, FLA

38KV

650 cfm is definitly enough for a 454"/330.

A 454" @ 4600rpm only consume 600 cfm.

Zanie

The smaller venturis make the carb work better at lower engine speeds. It'll be much nicer around the docks.

mcollinstn

I'd just put J-tubes on your 750 and if it has a mechanical fuel pump, you'll need to run the diaphragm vent to the flame arrestor (assuming it is a marine pump - if not, you'll have to replace it with one as well).

If your 750 is properly jetted and has properly sized powervalve in it, I wouldn't expect to see any measurable difference in fuel economy versus a marine vacuum 600/650 carb. As far as idle quality, they don't idle off of the venturi size. They idle off of the bleeds and idle fuel circuits. The throttle plates should be nearly closed.

If you happen to have access to a marine 650 for $50, then go for it. Otherwise save your money.

You are "overcarbed" but not to any substantial degree to matter.