Thread: 780 Holley Double Pumper Carb for the Street??

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This Carb was originally a 650 Holley DP.For years and years of tuning I got nothing but instant fouled carbon spark plugs.I must have gone through 100 sets.I finally went to a local speed shop and the owner told me that the Carb was to small for my Chevy 402 BB.So I gave it to him and he sent it to a company in Texas.They made it flow 780cfm's and put in a 4 corner idling circuit.Finally after all those years of looking at carbon fouled plugs it fixed that problem.The problem now is with Idling.Its a very touchy carb and if I set the Carb to Idle at 1000Rpm's as the engine gets hotter the Idling Rpm's starts to climb to around 1500RPM'S.I have heard that the Double Pumper Holley is not all that good for the street.I do have a healthy sized Cam in it.I have a 4 speed Muncie also.Duration At .050 is 248 and 248,595 lift on intake and exhaust.I am only going to be driving this car on the street and Im wondering if these Holley Double Pumper Carb's suck on the street??

I ran a 750 DP on my '68 GTO - (400 cid) with a very similar cam. No problem once I had it tuned.

I always had to set my idle with the engine at full operating temp, then baby it quite a bit when it was cold. Used a manual choke. What kind of choke to you have, if any?

Yeah, it was too much cam and the wrong gearset (4.10) for the street. It was tempermental, took a lot of tuning, had too much compression for pump gas, and got horrible mileage. The MT wrinklewalls I ran werenn't quite right for the street either. However, I didn't build it as a cruiser, drive it 200 miles to a car show, or putz up and down Dodge Street on Saturday night. I built it to be a crazy-ass, take-a-deep-breath-when-you-punch-it, whadda-you-lookin-at-buddy, over-the-top, holy-cow-what's-he-got-in-that-thing, stoplight bandit. That's what one part of the hot rod world was - and still is.

Jack
My motto back in the day was: "Too much is just about right."

Originally Posted by Henry Rifle

I ran a 750 DP on my '68 GTO - (400 cid) with a very similar cam. No problem once I had it tuned.

I always had to set my idle with the engine at full operating temp, then baby it quite a bit when it was cold. Used a manual choke. What kind of choke to you have, if any?

Yeah, it was too much cam and the wrong gearset (4.10) for the street. It was tempermental, took a lot of tuning, had too much compression for pump gas, and got horrible mileage. The MT wrinklewalls I ran werenn't quite right for the street either. However, I didn't build it as a cruiser, drive it 200 miles to a car show, or putz up and down Dodge Street on Saturday night. I built it to be a crazy-ass, take-a-deep-breath-when-you-punch-it, whadda-you-lookin-at-buddy, over-the-top, holy-cow-what's-he-got-in-that-thing, stoplight bandit. That's what one part of the hot rod world was - and still is.

Jack
My motto back in the day was: "Too much is just about right."

I don't have a choke on mine.Looking back now I should have stuck with a Cam that would work nice with a 3:73 Gear.Maybe a set of Aluminum heads would make up for a smaller Cam and the lower 3:73 Gears??I remember having a 500 lift Wolverine
Cam in the same engine and that idled great with 2:73 or 3:08 Gears and the car was very responsive with my Edelbrock Performer Manifold.It would have been alot better if I had the 3:73's.I would like the car to have power to get in the low 12's or high 11's even though its primarily a Street car.

I was also wondering when you said how bad your gas mileage was??How many MPG did you average??Your engine and combination seems very similar to mine.

Originally Posted by 69muscel

I was also wondering when you said how bad your gas mileage was??How many MPG did you average??Your engine and combination seems very similar to mine.

Somewhere between 4 and 10 . . . depending mostly on my right foot.

Most DP carbs run a progessive linkage and only run two barrells until you stick your foot into it. I've always ran DP and never had a problem on the street.

later

dennis

.....I used to run a Holley 750 double pumper on my 413 small block although I had a MUCH smaller cam. 222/232. This motor is being rebuilt now & the carb is being rebuilt at The Carb Shop in Ontario, CA. It sat for years so I'm having them rebuild it. It used to work great on the street except for it 'stumbled' {hesitated} coming out of the hole. The place is addressing this. But it idled just fine before..... Bill
Oh, I'm using a bigger cam this time, either 230/230 or 236/236.....

Originally Posted by dennis kelley

Most DP carbs run a progessive linkage and only run two barrells until you stick your foot into it. I've always ran DP and never had a problem on the street.

later

dennis

I was wondering if you were running a big Cam with the Double Pumper Carb??

I should have got opinion's before putting a 248/248 Cam in my 402 BB.I just thought the bigger the Cam the faster the car would be.(inexpierence i guess)

well the bigger the cam the faster the car is true.... as long as you build the rest of the engine with the cam specs..... i undercammed my first few high performance builds just because i was afraid of over camming

Originally Posted by thesals

well the bigger the cam the faster the car is true.... as long as you build the rest of the engine with the cam specs..... i undercammed my first few high performance builds just because i was afraid of over camming

Even though I have stock ported oval port head's the car makes good power from 2500 to 6000 RPM'S.I think though that this Cam could be killing my gas mileage and today that's somewhat important.I never had a working gas gauge in it to see how bad gas mileage was with my 402 BB.Its not fun getting less then 10MPG if the car is only driven on the street!! I know a smaller Cam would give it even better street manners and I could get rid of the 4:11 Race Gear's especially since I don't have an overdrive for it.

1150 holley idles fine at 1000. big cam 275 -287 @.050 drive it on the street runs ok much better at 4500 and up. what you need to do is open the back barrels there is a screw for this and back down the front idle screw you may be past the idle transfer slots on the carb and by cracking the back you will let more air and fuel and use the idle circuit this may help with fuel mix

Originally Posted by pat mccarthy

1150 holley idles fine at 1000. big cam 275 -287 @.050 drive it on the street runs ok much better at 4500 and up. what you need to do is open the back barrels there is a screw for this and back down the front idle screw you may be past the idle transfer slots on the carb and by cracking the back you will let more air and fuel and use the idle circuit this may help with fuel mix

Thats interesting and I will keep that in mind when I attempt to get it running in the next few day's.

I still run a 650 dp on a 302 ford and it has a mild cam and AFR 165 heads. The carb works so well on this motor its scary. Dual plane intake to.

later
dennis

Imo double pumpers are for the track, but there are guys out there who know what they're doing and run them on the street with a high degree of success.
As witnessed by a couple of posters above.

That said, I prefer vacuum secondary or air valve secondary carbs on the street.
Makes for a crisp running engine that launches well with mild cam or a fairly big cam.

The dual quad setup I was running on my 2400# 32 roadster utilized straight, non-progressive linkage to the 500 cfm Carters.
The 462" Buick engine responded well with the smaller carbs and tip-in on the secondaries was very smooth.
Kenne-Bell recommended dual 750's, but I elected to go with the 500's because my goal was to have an engine that responded well in the low and mid-range.

If I was building a drag race bracket type car I'd still run vacuum or air valve secondaries.
They are trouble free for the most part and since bracket cars don't need that last little bit of horsepower you can give up some and pay attention to driving the car rather than dinking around with it in the pits.
Kind of a change the oil and go racing car.

I pulled the dual quads and big cam to use in an upcoming project.
An Edelbrock Performer intake and 750 cfm Carter went on the engine along with a milder cam.
The engine responds well and mileage in town runs 10-12 mpg.
Highway runs about 16 mpg.
If . . . you keep your foot out of it.
The carb is jetted/rodded for the 3300' altitude I live at now and it still runs good when we go down the hill to the river at about 450' altitude.

Mileage could be better I suppose, but the 32 has the aerodynamic qualities of a brick.
Fun quotient is pretty high though....

Get yourself a street oriented carb for the car.
I don't have any experience with them . . . yet, but the new Edelbrock AVS carb looks like an excellent way to go for street use.

A quick perusal of jet sizes comparing the AVS to the AFB style has the AVS with slightly leaner jets/rods in comparable carb cfm ratings.
That would help in the mileage dept.


As a small aside, at times I run a mid-sized Holley with vacuum secondaries that is jetted fairly lean.
No gas mileage figures from it, but one strange thing noted was when running sans hood side panels on the 32 in cold weather you could park the car for five minutes and even with a fully warm engine the electric choke would kick on for the startup.
The Carter's electric choke never did that with the side panels off.

Both the Holley and Carter electric chokes operate as they should when the hood side panels are on in cold weather.

Funny stuff, just another one of those hot rod type idiosyncracies we run into with the mix and match of components we are wont to do with these cars....