Which Holley Carb to use???

[ghawkman21]

I have a 1997 Ultra Jet with a 502. It now has an 850 carb but it uses WAY too much fuel. What model can I go down to without losing a lot of power and performance? Holley.com says a 600 CFM. I went to the river and one trip about 30 miles I used 35 gallons of fuel. It costs me $120 for just one trip. Something must be wrong.. HELP!!!

[HammerDown]

Some will say the 850 is what ya need, personally I like vacuum secondary carbs. A 715 cfm works perfect on my 468 Chevy @ 5300 rpm. It gives my engine all the CFM it needs and it's pretty good on fuel consumption.
I have a 850 DB I tried...it did nothing but use MORE fuel > now sitting on the shelf for someone that (thinks) bigger is better :p (not always)

[502 JET]

I have a 1997 Ultra Jet with a 502. It now has an 850 carb but it uses WAY too much fuel. What model can I go down to without losing a lot of power and performance? Holley.com says a 600 CFM. I went to the river and one trip about 30 miles I used 35 gallons of fuel. It costs me $120 for just one trip. Something must be wrong.. HELP!!!
Make sure your power valves are good.If they are blown out/or opening too soon it could contribute to excessive fuel consumption.
When I was running a stock 450hp 502 with a 850 on it I would burn 12-15 gallons an outing.I never went more than 5 miles from the ramp.Cruising around at 3500+ rpms tends to burn alot of gas with any motor or carb combo.A vaccume secondary carb may help.But I will stick with my doubble pumper.

[enzo]

If you are interested...
I have a new 750 cfm Holley HP - at cruising speeds it works like a small carb but when youopen it up it flows better than your 850. The carb is months old - i am swithching to something bigger. Let me know - you can PM me.

[SmokinLowriderSS]

I'm with both the above. A vac secc will probably give ya the best mileage (like it'll EVER be good feeding a 502), and would go something arround/just above a 700 to not take too big a performance hit.
I'm running a 700CFM 4150 DP on my 454. Been told I need an 850 and I'll get more power .... maybe, but I haven't been convinced yet. I am certain it'll burn more gas tho, likely more gas than the more power I'd ever get.

[poncho-pwr]

It kills me how people come on here with their big block jet boats and are concerned with gas usage....Sell the jet boat!!! Seriously though, I understand but it's still funny as hell!!

[ERV JR]

I Dont Understand How This It That A Dp Carb Would Use More Fuel
Than A Vac Sec. Carb. I/e It Would Take A Given Amount Of Power To
Turn The Pump With The Load Of The Boat And Cruise At Say 35 Mph
So If The Engine Is @ 3500 Rpm It Needs A Given Amount Of Air And
Fuel To Maintain That Cruise Speed , So It The Vac Sec. Doesnt Open
Then U Need To Open The Primaries More And With A Dp The Sec, Will
Open With The Linkage Letting U Not Roll In To The Throttle As Much,the Way It Seems The Engine Draws The Fuel From The Boosters That It Needs To Go At That Speed So If It From The 2 Barrels Or All For Only Open A Bit Its Using The Same. Right ? The Only Extra Fuel I See Being Used Is From The Squirter But Thats Not Too Much. Does Any Of This Seem To Be Correct ?

['78 gt boat]

I have a holley marine 780cfm I believe with vac secondaries on a well built 460 BBF. I get decent hours out of a full tank but then again if you own a big ass motor should you not expect to spend a lot on fuel? :crossx: :crossx: It gets worse when I run 110 race gas at $6 per gallon. :220v: :220v:

[MudPumper]

When was the last time the pump was rebuilt????? If it has not been overhauled in the last 9 years, I would freshen the pump before messing with the carb. You will see minimal, if at all measurable, fuel economy gains by switching carbs. If the pump does not have good bearings, a straight shaft, and most importantly an impeller that is balanced and free of dings, it won't be working very efficiently. A fresh pump is an efficient pump, wich requires less throttle, which = less fuel. So the question is, When was the pump last rebuilt and what kind of shape is the impeller in?

[speed freak]

Just rebuilt my pump and fuel consumption went DOWN!!!!!! :cool:And I am running an 850 DP on a BBF 460!!!!!!!

[Cas]

I just went from a Weiand Team G single plane intake with a Holley 750 dp to a Edelbrock RPM Air Gap and a 750 VS.
With the Team G/DP, I could go about 2 1/2 hrs on 22 gals of gas with a 5000 rpm max. With the Air Gap/VS set-up, I can go about 6 1/2 hrs on 22 gals and I now get 5200 rpms. That is real time and not speculation with the comparison being made at 3500 rpm cruising .
Both carbs were set-up by Bigs Performance based on my engine specs.

[YeLLowBoaT]

Well my math says that if you had 100 VE your 502 spining 5000 rpms would you 726 cfm. So a 700 or 750 would work for you. If you go to a vacc 2nd carb you will save some fuel. (no squirters) You will see a big reduction in the use of fuel if you always on and off the throttle. If you keep your speed constent, you will really see no diff.

[22HotKat]

I have a Speed Demon 850 on my ZZ502 w- Legend Pump "a" impeller
Mech secondaries - Not a gas guzzler unless I bury my foot the the gas gage moves faster than the tach
I think you have some tuning issues. Do the secondaries open before the or just after the boat planes? - The power valve is suspect - run a vacuum gage and run a PV # 1/2 the idle vacuum. I don't think a 750 is your answer

[jtmarten]

I'm running a 750 vac sec on my mild 454. 23', heavy hull daycruiser with a bottom in need of strake repairs, and I get just over 2mpg cruising at 3200rpm with 4 people and gear on board. My secondaries open at 3800rpm, sooner if pulling a tube.