Iv’e fiddled with the rebuilt factory quadrajet on my 71 for about 7 years now and am finally kidnda sick and tired of it. I have made a decision to swap over to a genuine double pumper mechanical secondary carb that will give me the snappy throttle response I’m looking for and would like a recommendation for a good double pumper make/model that will fit properly (gotta watch the height for hood clearance with the RPM Performer on it) on that slightly modified base motor and swap nicely onto a 383 I’m building for later. No EFI for me.

 

You cannot bolt a double pumper directly to the intake the Q-Jet came off of and if you use an adapter you will have more problems with running than you claim to now.......to use the square bore Holley you need to swap intakes.......
A double pumper Holley is not going to be any more "snappy" than any other carb that is tuned correctly....especially not a Q-Jet......and the carb is no taller than what you have now.......
But if you are looking for an overall solution then I don't recommend the Holley DP......use a 2101 Performer intake and a 0-90670 Holley Truck Avenger.......if this engine is relatively stock...there is simply no better out of the box carb you can buy for a mild 350.....
If the Q_Jet you have is the original.....there is no better carb for your Vette.......it just isn't functioning properly.....or your ignition timing is way off......90% of all carb problems are timing. If this Q-Jet is a commercial replacement then you need to throw it in the trash and start over.
I build Q-Jets for people with older engines that do not want to replace the intake......there truly is nothing better than the stock unit.....on a stock engine.....

Jebby

 

Is the RPM Performer a 7104 that the Quadrajet is mounted on?

 

Didn't catch that.......my bad......

Jebby

 

Hadams,

I'm like you. I like the quick throttle response of a Holley double pumper. Never been a big fan of vacuum secondaries. And that is why I will not run a Quadra or a truck carb.

Take a look at All State Carbs web site. Click on the Holley High Performance link. They sell new, rebuilt and remanufactured 4150s model 4777 D.P. for less than $400 rebuilt. However, I believe they want a core. I am not giving anyone my old carb, ever.

 

I personally like proform race series carbs.

https://www.summitracing.com/parts/pro-67200

 

https://www.summitracing.com/parts/hly-0-6210

There ya go. Double pumper spread bore. They've changed a bit since the last time I bought one 50 years ago.

 

Problem with the old 60s tech 47 series DP holley you get next to nothing in adustment 4 corner idle is it. No removable air bleeds and no channel restriction adjustment. To get both in new carbs holley or there copy brands there around $850 to $1100.00. But if that price tag not a problem you can end up that adustability plus billet metering blocks that dont have the cast perosity problems of old, billet base plate and what a good street DP should have annular boster's. Plus a lot of other stuff im not mentioning.

 

I find vacuum secondary carbs soggy.
Allstate carburetor is a great choice. They will set it up for you and it will be close.
nothing horrible with the qudrajet just everything for them is drying up.

 

Agreed. There are multiple scenarios here.

If it is still original; both carb & engine, you will not find a better carb than a QJet. Repairing a Quadrajet for a stock engine can be done if the QJet has not been commercially rebuilt. They run near as good as EFI without the hassle. Better MPG than any other carb also.

If it has been locally rebuilt, and OEM jets & rods not lost, then more than likely Jebbysan, Lars, or Cliff Ruggles can get it running to OEM perfection. There are almost no other "carb shops" I would hand one of these carbs over to these days, as both the knowledge and the parts cache is quickly being lost forever. They do need to be carefully adjusted to not "bog", but once set, are dead reliable for 50-100k miles.

If it has been commercially rebuilt, in the past they haphazardly mixed & matched parts and it is very likely permanently ruined and you will never be able to get it to run correctly.

If your engine has been modified, even by something as simple as a slightly bigger cam, it may be very difficult or impossible to tune an original QJet to run well. The supply of common upgraded jets & rods parts has almost completely dried up. If one of those 3 guys can't fix it, then you need a newer Holley, QED, etc. that still has parts readily available for it. QJets don't like big cams, it's too hard to adjust them enough.

If you have a street car that bogs, or the throttle is not snappy, you have a tuning issue. It could be the carb, the distributor, the camshaft, the tuning, or just the combo choice of all 3. IMO there is zero need for a double pumper on a street car. For a racer, yes, absolutely. A carb should never bog. It is just that most of the guys that tune carbs these days, are racers, and they tune Holleys, and they use DPs, and they run big cams. So that is what they are most familiar with. They don't often work on or like vac sec carbs. The newer model DPs do have a lot more adjustments that the older models did not. Because that is where the carb market is, and that is where the new features are demanded, and introduced by the mfgrs. A lot of "racers" know how to tune these DPs, but many only think they know how. A DP goes well with a big cam, but it will never be as street friendly as a milder cam.

There are not many carbs, of any type, that are a bolt-on and run well situation. Jebby's recommendation is one of the few. It works well for a medium strength street engine. All other carb setups require some degree of fine-tuning, some a lot.

You might want to list your entire engine combo here so some of the experts that visit here can give you some better advice.

 

The 47 series DP that gets the race car reputation carb all of them were set up with more fuel flow at idle to use with low vacuum at idle race cams. So you put one on your milder then race cammed engine that has better vacuum pull at idle now you end up with way to much fuel at idle. You can buy for $675.00 a street calibrated holley hp DP that at least has removeable air bleeds but not channel restriction adustment. But i doubt over rich idle problems would happen with it because holley has set the carb up as advertised as a " STREET " calibrated DP carb. Another problem gave DP some bad rep is people using to big of one on single plane manifolds. Vacuum secondary carbs the engine is only going to pull what it needs in air so if you over carb with it no big deal in comparison to big a DP carb. Nothing wrong with DP carbs for street engines if you use some sense to your choice and duel plane manifolds are not sensitive to carb sizing like single planes are.

 

I ran a spread bore Holley with mechanical secondaries on my 68 427/390 on the stock intake. Easy bolt on. The car ran fantastic.