can anyone tell me why a vac secondary is NOT a good idea on a jet boat and why a double pumper is
If you want to haul ass all the time(or have a big hp motor), you want at least an 850 double pump. I have a 460 mild cam with a holley 750 vac secs. fuel pressure holds at 5.5 psi. When krusn the mains are flowing = gas milage. When I stomp on it the secs open up and sucks the gas up. A double pumper will dump gas all the time, regardless of krusn or haulin ass. So ask yourself, what do you want to do or have as a motor?
i disagree...u can stay on the primary's for along time before u start to feel the secondary's start to kick in...there are alot of peeps who run 750's & smaller mech sec carbs with great mileage ...if the gas thing is an issue, why own a boat?...also...u could try the Edelbrock 750cfm...small pri, lg vac sec...rite out of the box, they run great...i have run one with good results (mileage, power)...just my .02 centsA double pumper will dump gas all the time, regardless of crusing or haulin ass. So ask yourself, what do you want to do?
disadvantage is that you'll need vacuum to open up the secondaries off the line (time delay). DP's you just shove the go pedal and your off. Jet's load and go right way - unlike a car where you'll often see a bog off the start.dont care about the mileage to much just want to know which one is more efficient and whats the disadvantage is running a vac sec 750 holly
The disadvantage of a properly adjusted vac. seccondary carb in a jet boat is a SLIGHT loss of power, because it will never be too big, and generally be just a tad too small for the engine demand.dont care about the mileage to much just want to know which one is more efficient and whats the disadvantage is running a vac sec 750 holly
I'm one of the guys with "too small of a mech. seccondary carb", at least according to the guys who swear "850 or nothing". 700CFM 4150 Holley, primaries only untill about beyond 4,000RPM. With good water, my wife & I can cruise at that, making 45mph, and do mighty good mileage-wise. HEAVY old Taylor boat.i disagree...u can stay on the primary's for along time before u start to feel the secondary's start to kick in...there are alot of peeps who run 750's & smaller mech sec carbs with great mileage
This steps over into cars, but, many, many years ago, I had a '74 Camaro, 400 small-block, 600vc holley (list 3310 if I recall right), TH400 automatic, 3.73-ish gears.Also, there's a misconception the vacuum secondaries run off engine vacuum, they don't. Vaccum secondary carbs use the high venturi vacuum in the primaries to open the secondaries. That vacuum will increase with airflow. You can change the vacuum level by changing the springs in the dashpot or you can get an adjustable dashpot so you won't need to change springs for different opening rates. I went with the adjustable type due to I like making things simple. If I knew I was going to be doing a lot of cruising, I'd turn the adjustment screw in about 1/4 turn so the secondaries wouldn't come on too soon. Turning the screw back out would allow the secondaries to open sooner and quicker.
I like the fact I could get decent gas mileage without losing any top end with the combo I have.
that's what it's all about right there!It is all about how the combination fits together.
That's why I've been using Bigs Performance, each carb is built specifically to your engine specs and is dyno tuned before it's shipped out.i wish it was all abit easer with no spicific equasion to tell you what to run it just seems as if you need a dyno and a hand full of carbs diffrent sizes, diffrent designs and play for a day.