need help selecting a carb

[endeavour32]

My brother is running a carter/merc 750 off a 454 mag on his 355 w/vortec heads. The boat runs great with it!

[87MagnumII]

thanks guys for all the input!! im leaning towards the holley 650 qjet replacement, im thinking it has vacuum secondaries. somebody mentioned earlier to go with mechanical secondaries. was wondering about the pros and cons of mechanical and vacuum secondaries

[fkboatman]

transition into seconderies is alot smoother and no lag

[kornegle]

I have a similar combination but with aCOMP marine 212*/218*,.450" lift flat tappet cam. Are you sure that off road GM cam has low overlap to prevent reversion? I kept the stock Quadrajunk and it seems to fine. 216 Wellcraft Eclipse went from 52 - 53 gps to 60 -61 gps after the heads, cam, intake, etc.

[sprink58]

I vote for the Holley.

I like the 600 CFM Mechanical Secondary set up for that boat. The throttle response will be very crisp and you have complete control over the secondary action. The next step up with Mech Secondaries is the 750...which is too much carb for the motor.

You want to keep the velocity up as high as possible to keep it crisp.

My brother has a similar set up in a Formula F3 355/Alpha GenII w/ a 600 Double Pumper on a Edelbrock ES Square Bore Performer.

The throttle response is like NOW and he can plane the boat and then back off and cruise on the primaries. Very sweet set up.He gained 5 MPH over the Q-Jet and saved about 10%~15% on the GPH (once he started driving it like a SANE person)

I wouldn't run 750's on a SBC unless it was a 383...too much air flow at RPMs under 5500~6000 for a 350...makes it sluggish.

[87MagnumII]

ended up going with a 650 marine demon, havent fired it yet but i will let you guys know as soon as it warms up in april!!