What exactly is a "double pumper"?

SadbutTrue · Jan 6, 2004

I see a lot of people running 650cfm Holley Double Pumpers around here... what does a double pumper do differently from a standard carb? And would a 650 DP be too big for the engine in my sig? I was gonna pick one up from a friend for 20 bucks and rebuild it, definitely to use with my next engine but if it works with my current one I might as well throw it on and sell my edelbrock.

Thanks

D.Hearne · Jan 6, 2004

D.Hearne · Jan 6, 2004

A double pumper carb is simply a mechanical secondary carb that has two accellerator pumps, one for the primary and another for the secondarys. And yes it will work on your motor

pabear89 · Jan 6, 2004

And your running an auto, so set the rear pump lever gap slightly larger than the front. +.005 or more to eliminate any sec bog.

I'd run the Holley over Eddy any day,
But that me.

PB

68GEETEE · Jan 6, 2004

better response with mechanical secondaries, great for racing. For the street a vacuum secondary might be wiser as it is a bit more effecient, gas mileage wise.

I run a 600 cfm double pumper on my 302, lots of fun, except when its time to put more gas

SadbutTrue · Jan 7, 2004

I've never been completely clear on whats needed to run a mechanical secondaried carburetor? would it work just bolting it on? or would I need to do other things to it?

SadbutTrue · Jan 7, 2004

hearne, by "work" with my motor, i meant to say i was thinking it might be too big (though you might have gathered that). Sorry, I got a bit lazy with the description of my question.

D.Hearne · Jan 7, 2004

No, it won't be too big. I'm running one right now on my "spare" roller 5.0 in my Ranger. This motor is one I slapped together from a shortblock out of a wrecked 93 E150 van. I swapped the stock base roller for an F4TE roller ( this is the cam that comes in the 94 up E & F series vans and trucks and the V-8 Explorer/Mountaineers) Ported E7 heads with Cobra 1.7 roller rockers, Shelby type tri-y headers, A Ford A321 high rise dual plane intake topped by the 650DP Holley. As 68GEETEE posted, your gas mileage may suffer compared to a vac. sec. carb, but the response from the secondaries will be faster.

69stang351 · Jan 7, 2004

68GEETEE said:
I run a 600 cfm double pumper on my 302, lots of fun, except when its time to put more gas

mfp4073 · Jan 8, 2004

why do yall aways answer questions with jargon?......ok...double pumper over vacuum advance. These are both 4 barrel carbs. The double pumper uses mechanics to open the rear butterflys/secondaries. These are the ones in the back. with a mechanical at a certain throttle position/pedal position the secondaries are open a certain amount. With vac advance secondaries the carb uses vacuum pressure in the manifold to sense when to open the secondaries. The good is that vac advance secs will close off and save you gas at a certain point, but they lag to open when you stomp the gas. Double pumpers open completely, and right away when you put the pedal to the floor. My 289 is running a 650 double pumper and in third gear (toploader manual) I can stomp the gas at 50 and chirp the tires. The response with a vac advance secondary would be delayed and not produce the same automatic response.

That help?

D.Hearne · Jan 8, 2004

mfp4073 said:
why do yall aways answer questions with jargon?......ok...double pumper over vacuum advance. These are both 4 barrel carbs. The double pumper uses mechanics to open the rear butterflys/secondaries. These are the ones in the back. with a mechanical at a certain throttle position/pedal position the secondaries are open a certain amount. With vac advance secondaries the carb uses vacuum pressure in the manifold to sense when to open the secondaries. The good is that vac advance secs will close off and save you gas at a certain point, but they lag to open when you stomp the gas. Double pumpers open completely, and right away when you put the pedal to the floor. My 289 is running a 650 double pumper and in third gear (toploader manual) I can stomp the gas at 50 and chirp the tires. The response with a vac advance secondary would be delayed and not produce the same automatic response.

That help?

Wait, If I'm not mistaken, he didn't ask what the difference was between a mech. sec. carb and a vac. sec carb was, and I also responded with the part about the mech secondaries, and they are not neccessarily always 4 bbl carbs, the Holley 3 bbl comes to mind ( or have you heard of that one) Or how about the Holley 2 bbl that also has a primary and secondary side? Maybe i just assumed he wasn't as ignorant as you think he may be, when it comes to carbs?

SadbutTrue · Jan 8, 2004

How much difference in gas mileage would there be? I can take a mpg or so less, i'd also imagine on long trips the mileage would be roughly the same since i'd rarely, open the secondaries.

But outside that, there isn't anything really special to do hooking it up? i've never had any experience with mechanical secondaried carbs before.

D.Hearne · Jan 8, 2004

They bolt on just the same as any other vac. sec. carb, mileage difference depends on how much you like to floor it and whether or not the carb has 30 or a 50cc secondary accelerator pump. ( that's 60 cc's of gas down the hole each time you nail it with twin 30's and 80cc's with a 30 & a 50) Ther's nothing tricky about them other than setting the gap in the pump arm so the primary side opens as soon as the throttle blades move.

mfp4073 · Jan 8, 2004

D.Hearne said:
Wait, If I'm not mistaken, he didn't ask what the difference was between a mech. sec. carb and a vac. sec carb was, and I also responded with the part about the mech secondaries, and they are not neccessarily always 4 bbl carbs, the Holley 3 bbl comes to mind ( or have you heard of that one) Or how about the Holley 2 bbl that also has a primary and secondary side? Maybe i just assumed he wasn't as ignorant as you think he may be, when it comes to carbs?

Sadbuttrue, I am sorry that I thought you were ignorant to what the differnce between a double pumper and a vac advance sec carb was. That was my fault for assuming and in the future I will think twice before I try to offer my help

SadbutTrue · Jan 9, 2004

mfp... lol i dont think hearne meant it that way, but in any case i am a confessed newbie to all this stuff, so feel free to be as blatantly dumbed down with your explanations as you want.

hearne are secondary pumps labelled in some way as to tell me whether its a 30 or a 50?

D.Hearne · Jan 9, 2004

The cover for the 30cc pump is about a 1/4" thick and the 50cc about 3/8" thick, also the 50 has a different pump arm. Sorry I can't post pics here ( ain't figured that out yet, still) but if you'll look up a picture of a Hollley 500 cfm 2 bbl, it'll have the 50 cc pump ( under the fuel bowl) Most Holley 4 bbl carbs come with 30cc pumps. Some have a 30 on the primary side and a 50 on the secondary side, then the full race carbs sometimes have twin 50's.

D.Hearne · Jan 9, 2004

mfp4073--- I'm sorry if I came down hard on you, but your post about my and the other's replies about posting with "jargon" was way off base in my opinion. Your explaination about the differences between a vacuum sec. and mechanical sec. carbs was a good one though.

slapper · Jan 9, 2004

SadbutTrue said:
How much difference in gas mileage would there be? I can take a mpg or so less, i'd also imagine on long trips the mileage would be roughly the same since i'd rarely, open the secondaries.

There will be a noticable difference, if left unaltered or modified.
Holley increases the primary jet about 4-8 sizes in the 4150 dbl pumpers, and leaves the Power Valve Restrictor Channels,(PVCR), small.
You can obtain much better streetability,(gas mileage), without running too rich,(common complaint about dbl pumpers on the street), by reducing the primary jet sizes, and then opening up the PVCRs slightly with a small pin drill. As you know the PVCRs are the small holes located under the power valve.
You'll get the additional fuel flow required when the power valve opens, but not run unnessesarily rich while just cruzin.
There's no reason to open them up past say 3/32", unless you're REALLY intending to meter some fuel upon throttle application.
I've been told that they do not offer additional fuel flow if opened up past 3/32" without further modifications to the emulsion wells.

mfp4073 · Jan 10, 2004

D.Hearne said:
mfp4073--- I'm sorry if I came down hard on you, but your post about my and the other's replies about posting with "jargon" was way off base in my opinion. Your explaination about the differences between a vacuum sec. and mechanical sec. carbs was a good one though.

Hey d...how about this....seems like we may have both gotten a little bit off using the typed media that does not play out nuances as well as being there in person ...I was not trying to rag on or be an ass...I was more going for a chuckle and messing with as i didnt think that his question had been truly answered in what is sounded like he was looking for. Just tryin to get to what it sounded like he needed.

You must admit that people get to talking "code" to someone asking a question about something they dont know...I once read a thing describing a conversation about a mustang that just had a bunch of "scj, notchback, kcode, factory disk, toploader, 9inch, shaker" type references in it. Most would have no idea that a car was involved!

k, shake hands and cool with all....was not meaning anything more than a ribbing with "jargon"

D.Hearne · Jan 10, 2004

mfp4073-------- I hear ya

What exactly is a "double pumper"?

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