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."

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

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.

.....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.

my reccomendation would be same thing i did..... forget about gas mileage at all on your classic, you're never gonna get good mileage.... make it your fun car.. drive it maybe 2 times a week just to cruise or go out with a lady or such... and for the rest of the week buy a little beater thats dependable, and gets good gas mileage.... i myself bought an 89 nissan sentra.... its not pretty, and it only has 90 horsepower, but after tuning it the best i could.... i get 42 MPG

69....

I have run a 750 double pumper on a 70 Z/28 with fine results just as the other guys here are saying.

Question: how can some outfit turn a 650 double pumper into a 780 double pumper? I'll tell you how: they piled up a bunch of used parts that included the body of a 780 vacuum secondary carb. They added the bowls from your 650 DP, etc. The carb is probably a mismash of parts....did they know what they were doing? If the carb doesnt run right, then the answer is _______
(insert answer here).

mike in tucson

Well I don't no exactly what all they did to the(650DP to flow 780) Carb other then put a 4 corner Idling Circuit, because it was many years ago.I have tried 2 Holley Double Pumper Carb's but regardless of the tune my spark plugs alway's were carbon fouled.I had new MSD Ignition,Coil,Plugs,Advanced Timing at Idle.The one thing it did was run great with Nitrous the first time I used the NOS System.After that I had the carb sent out to Texas to cure the fouling of the plugs.Now with the Nitrous I get instant detonation luckily my engine parts are Forged.

Originally Posted by thesals

my reccomendation would be same thing i did..... forget about gas mileage at all on your classic, you're never gonna get good mileage.... make it your fun car.. drive it maybe 2 times a week just to cruise or go out with a lady or such... and for the rest of the week buy a little beater thats dependable, and gets good gas mileage.... i myself bought an 89 nissan sentra.... its not pretty, and it only has 90 horsepower, but after tuning it the best i could.... i get 42 MPG

I never really worried about gas mileage until these 2 last years.Only because this is not meant to be a race car.I would like to think I could get at least 10mpg with a 402 BB but with the rather large Cam I have who knows

The one thing I don't have is a choke on the carb.I wouldn't think that would matter on a 90 degree day though.Im afraid to take it out on the road until I can get it Tuned and Idling correctly.I could live with the big Cam even though it has a Lopey Idle.Just need to find the right Carb.