tiago

I bought a jet boat with edelbrock street tunnel ram and 2 1850/ I guess 600 cfm carbs, vacuum secondary with side hung floats. they are old and leaking, I want to replace them but I was told by jegs to use 2 double pump carbs with center hung floats. I am concerned about washing cylinders. has comp cam 568/ 578 lift and 292/296 duration, give me some advice, thanks

Swiley383

I have read vacuum secondary on a tunnel ram won't work right due to low vacuum. Contact Holley or Quick Fuel or some other carb manufacturer and see what they say.

mytmouz

My old boat had twin 850's on it, and I didn't have any issues, other than keeping fuel in the tank...

lg406

Not true. Manifold vacuum has nothing to do with vacuum secondary. In fact it is recomended you use VS carb on your setup. BTW: 1850 holley is a 600 cfm carb.

BigBlockMark

I would consult a well known custom carb builder and have him spec and build you carbs. Less grief in the long run. Mark Whitener in Orlando Florida is who I recommend. Just google jmarkaudio. He also has a fuelsystems forum online. He has helped me on custom engine carbs..Prices of new Holley carbs are going up again March.

TheodoreThompson

I’d be a bit careful jumping straight to dual double-pumpers. In a jet boat you’re usually under steady load, not snapping the throttle like a drag car, so vacuum secondaries can actually work fine if they’re healthy. Your old 1850s leaking is more of a rebuild/condition issue than a design flaw. Double pumpers with center-hung floats give better fuel control and response, but they reef-spins3.com can be easy to overfuel if not tuned right. Cylinder wash only happens if it’s way rich. I’d say either rebuild what you have or go DP but keep jetting conservative and tune from there.