carb. help
 

have a 454 stroke to 496 with 9to1 pistons ,60's over, heads large oval with 1.88exh. and 2.19 intake dual plane airgap ,cam 542 lift ,850 cfm/to 870cfm holley .then added m-2 procharger with 5# boost. elect. pump with 8 to 9 # pressure it seams that i am not getting enough gas to secondary have 92 in front and 99 in back which we drilled out to 140, back only, still not getting enough gas when running exh temp go up. plugs are white, do i need a drifferent carb. or can i mod. this one?

If you don't have 1/2 inch fuel lines on boat I would change them. I had the same problem a few years ago went with the SX pump and went from 3/8 lines to all 1/2 inch fuel lines. I went from running lean with no sec. jets to jetting in the mid 90's.

carb
 

kchotboat, thanks we did change the line to 1/2" from inside tank too pump too reg. to carb split.

Call procharger and ask for Mike Chromer. He is the best person there to trouble shoot problems.

carb. help
 

called procharger and was told to put a 750 cfm carb. on and then jet it up. what i don't understand is that is going down on size. 850 not big enough go to 750? help me to understand this!

When you try to push over 50 gallons an hour of fuel thru a stock carburetor, problems can develop. You should have 5 to 6 psi fuel pressure going into the carb at wide open throttle, the pressure at idle is almost irrelevant. Next, can this amount fuel pass thru the needle and seat combo you have? Larger seats are available. Can this fuel get thru the metering block passages? We have run some excellent dyno pulls without any jet in the hole!

If your carb is in a pressure box, your fuel pressure has to be 5psi more than your boost presure at top end or your pushing against the boost. You probably know this.

If your not knowledgeable on carburetors, send it to Dean Nickerson or the Carb Shop, or by a carb set up for your specific application.

Until you get this sorted out don't run it hard or you'll need a new motor and the modified carb.

Yes, I am an ex - carburetor engineer, Goodluck, JB

I secind the recomendation for Dean Nickerson. Everyone I have sent to him now sez"it starts & runs now like it was fuel injected"! No soot from being too fat & no lean conditions either. He will rework the carb body, metering blocks, air bleeds, jets, and machine the venturi & flow the carb. His work is top notch!
And he will even TALK to you if you call!!:cool:

The reason they recommended using a smaller carburetor is that carburetors work by the pressure differential created by air velocity. Your engine will move the same amount of CFM at a given RPM, with the smaller carburetor venturi the air is now travelling at a higher velocity. This creates more of a pressure difference (or vacuum signal) and will pull more fuel.

This makes some sense but flowing enough gas thru a stock 750 for over 700 horsepower is very marginal. The metering blocks and inlet needles become restrictions rather than the jets.
another $.02

carb. help
 

i want to thank John B. & Rum Runner & blowm formula. this weekend drilled out back to 160 if this work ok. if not than i will send it to Dean Nickerson. thanks again for your help