I just purchased a 1993 32' Envision it has 2 454's that have been built. to what extent i don't really know. The last owner told me thaey were 500 bhp each. At the moment it has holley 650 dual feed double pumpers with mechanical secondaries. Right now it likes to stumble when you give it full throttle from off idle. I was wanting to change carbs but to what I have no idea. Any Suggestions???

Sounds like you need vacuum secondaries... or bigger jets for the accelerator pumps.

I wouldn't worry about the carbs. If you keep doing that you'll be needing drives.

You need to play with the accelorator pump cams and taylor the pump shot. This could involve new squirters as well. I had a simular issue with my 468, I changed out to an 830 cfm (from 930).. My 2 cents

What Griff says, or If your not carb litterate, like me, you send them along with your motor specs. to www.pro-system.com Belive me it's the best money you'll put in your boat!!!

I second what Griff said Believe it especially if you straighten out the carbs .

Call Dean Nickerson in Bristol, PA. He is a great marine carb man.

I wouldn't waste the jingle on those carbs. Buy some 800cfm holley carbs. That is what merc put on all mild performance engines like the hp 500, 420 etc. 650cfm is theoritically size properly, but in practice will be restrictive in my opinion.

BT