VI Cutty

Friend of mine is selling a "nearly new" Holley 750 double pumper. (that's all the description I have of it at the moment). My question is whether I would see any significant performance/power improvements with that carb, and what would be needed for installation? It came off an '85 442 with SBO 350.

I currently have a stock '71 350 with dual exhaust and what I believe is the factory QuadraJet. I'm planning on changing the cam this year to something like an RV cam but don't have any other significant engine upgrades planned for the near future.

My engine hesitates when coming off idle but in all fairness it sat for years and I haven't given it a proper tuneup. The QJet was supposedly rebuilt by someone who knew their way around the carbs but that would have been many years ago now, even if not a lot of miles. I understand the accelerator pump likely needs replacing and could be the culprit causing the hesitation.

Would it be worth considering the switch, or am I just as well off to stick with the Quadrajet?

If I were to consider the Holley, what else do I need to know about it to ensure it's right for my engine?

oldcutlass

I think it would be more carb than you need. Plus you would have to change your manifold. A double pumper is better suited for a manual transmission.

VI Cutty

Thanks Eric.

He's also selling a Holley 600 with vacuum secondaries and an Edelbrock 600 Performer which I also assume would need a new manifold (which I'm not interested in doing right now).

Would I be correct in assuming that neither of these would be an improvement over a nicely running Quadrajet?

I'm just exploring options and trying to get a bit educated...my gut sense is that sticking with the Quadrajet is the right path for now.

don71

I think your gut sense is telling you the correct thing.

oldcutlass

I'll be honest with you, in your application the quadrajet is your best carb without a manifold change even with a mild cam. Edelbrocks and Holleys have their following and they are great carbs. All carbs have their little quirks and all can be made to run great.

oddball

For a stock build, all carbs will perform very similarly IF they are properly tuned and in good shape.
Holleys are really common, so it's easy to get parts and advice.
Edelbrocks are really simple, so it's easy to futz with them.
Qjets are pretty complicated and got a bad rap, so it can be hard to get it set up right.

The Qjet is a really good all-around carb that can be adapted to almost any engine - just look at how long GM kept it going!

So it depends on your goals and how much time and money you want to invest. I'm a huge qjet fan, but the learning (and investment) curve is pretty steep. And there are some that I still can't get to run right.

techg8

Stick with the Quadrajet

just have it gone through by someone who knows what theyre doing.

Even a stock engine can see good performance gains (throttle reponse and power) when the Qjet has been recalibrated for performance rather than economy and emissions.

Some Qjet builders with good reputation:

www.everyday-performance.com
www.customrebuiltcarbs.com
seam murphy induction
Cliff ruggles

brown7373

Although the Q-jet may be more complicated, I don't think they are so complicated that a reasonably intelligent person can't rebuild one. If you were also talking about doing major carb mods, than maybe not. Get Doug Rowe's book, or better yet, Cliff Ruggle's book on the Q-jet. If you follow the illustrated, step by step rebuild, and keep all the parts in an orderly manner, it's not that difficult. Some people use an egg tray, some use zip lock bags.


Keep it stock with maybe a recommended jet/rod change and it will give you a good result. I currently have 3 old cars running Q-jets and they all start, idle and run smoothly and responsively at all engine speeds. And an original Q-jet lets you use all the original linkages, choke, cruise etc.

VI Cutty

Thanks for the input, all. I'll be sticking with the QJet - there aren't any compelling reasons to consider a swap and no reason to condemn the one I've got now.

As soon as I get a *koffVWkoff* running and out of my way I'll be getting serious on the Cutlass with a good tuneup, compression check, fluids change and attention to the carb. There are a number of little things that need doing and work on the QJet will be high on the list.

I don't see any immediate need for modifications, just a good cleaning and adjustment for now all of which I'll tackle myself...and if I'm lucky I'll be able track down a local QJet expert.

don71

Yea, sometimes we need a little German engineering in our lives, just beware of the liquid cooled alternators those jokers like to use now a days..

VI Cutty

No worries there, I only roll air cooled on the German front!

oddball

Installing a rebuild kit in a qjet is easy.
Getting all the funny adjustments right requires particular attention. Not hard, just kind of unusual and too easy to skip.
Noticing things that are wrong, broken, or missing can be quite a bit harder.

wcourt3010

you'd just need an adapter to put that edelbrock on.

VI Cutty

Good to know, but what would the benefit(s) be?

I'll give the QJet a reasonable chance before I consider other options for now ;-)

wcourt3010

i wasn't speaking to any benefits of the edelbrock over the Qjet, was just saying an intake manifold swap isn't necessary. there are experts on here who can way in on one carb over another, search the past posts its a popular topic, almost as popular as cam selection threads

qjets are great.

Destructor

I rebuilt a few Q jets with no problems including the computer controlled Q jet. I adjusted the new float level and the idle screws. I took it apart and put it back together with the new parts after giving everything thorough cleaning. If you have successfully built a model you can rebuild a carb, though I didn’t have to deal with worn out throttle shafts and I did have a shop perform final adjustments on the Computer controlled carb.

VI Cutty

I've successfully built models ;-)

finished2_zpsf88cc8a6.jpg

I've rebuilt old VW carbs in the past (amongst other things) so I'm familiar with the concepts - just not the nuances of the QJets. I'm probably at least a month away from doing anything on the car so lots of time for some edurmacating. There seem to be some good writeups available online which I've been have a look at too.

wcourt3010

this is a good book on the qjet. enjoyed reading this on a camping trip last year.

Destructor

Nice looking model.

VI Cutty

Thanks for the link, I've seen other mention of that book and his expertise with the QJets and will likely pick it up this weekend.

He also has a tech forum: http://www.cliffshighperformance.com...machinesforum/

Seems to be a fairly detailed rebuild guide here as well: http://www.crankshaftcoalition.com/w...4MV_carburetor

VI Cutty

Thanks...started out as a 1950 hard top. Cut the roof, dechromed the sides, lowered the suspension and tucked in some bigger chrome rims. The plug wires run under the valve cover plates. Was a fun build.