What are suggestions for a great street preforming carb. I have a 383 stroker, with a comp cam 270, edelbrock manifold, headers, 700R4 trans,edlbrock alum head.

Currently I have a holley street avenger 770. I am having problems tuning the carb and I believe that it has too much cfm for my vette. It is running rich. I would like to sell this carb and try a different carb. Many Thanks

 

try looking at edlebrock... i had a 600cfm with manual choke... ran like a champ right out of the box... plus the chrome finish looks nice...

 

The carb you have is not too big for you and should be pretty easily tunable for your needs. But if you want to try something else thats pretty easy to switch to, one of the Edelbrock carbs will bolt to your intake and typically runs pretty well out of the box.

 

A 770 is a bit on the large size, but this has nothing to do with it running rich. Symptoms of a too-large carb are poor off-idle and low-rpm throttle response.

Don't change the carb - find the problem. Can you provide more information on the problems you're having tuning?

 

I've been reading a lot on different carbs lately & basically the Holly has the same power as others, it just dumps a little more gas because it doesn't have as many parts to tune, when compared to a Q-jet for example. I would imagine a little rich would be normal but you're standing there smelling it & can tell more about it.

 

The key thing in your request is STREET. You want a Quadrajet. The Holley will never give both performance and fuel economy. Neither will the Edelbrock, which, while reliable, is a design deemed obsolete by GM in the '60s.

The Quadrajet, properly tuned, will give performance equal to any other carb, but will also give optimum fuel economy for street driving. None of the other carbs have the technology to do that, in spite of what anybody might say to the contrary.

God bless, Sensei

 

Come on now, Sensei.
If he cant tune the Holley, what chance does he have with a Quadrajet.
The Q-jet is a great carb and all, but it does have a bit of a learning curve to figure it out.

 

Man I hate these threads.....

 

Who says he has to do it himself? Besides, if you are going to learn, you might as well learn on a Q-jet. It's not rocket science and if you can work on a Quadrajet, you can work on any of them.

God bless, Sensei

 

I am a Qjet fan myself. I had help from the Qjet king Cliff Ruggles @ Cliffs Qjets on the internet. Give him a call, he always has a few minute's to help answer questions. He also will rebuild your carb, or send you parts to do it yourself. Al

 

I'll agree the Quadrjet is a fine carb, but to say you can't get both economy and performance out of a Holley or Edlebrock (AFB) is just plain wrong. My 64 SS has a strong running 350 with a Carter Competition AFB on it. I can get 18 MPG with it on the highway.

My 80 Vette with the motor in my signature gets close to the same cruising and it is a beast. Drivabillity on both cars is great. You just have to tune them! There is a lot you can do to tune both carbs. Just because most people don't spend the time tuning they should (or know how to) doesn't mean the carbs are bad!

 

ANY carb, properly sized and tuned will deliver very nearly the same results. The key then becomes....correctly sized and tuned.

This carb is not too big. As a comparison, the Q-jet typically flows around ~780 CFM.

The Q-Jet is a fine carb overall and a great street carb with the spread-bore configuration...but tuning one is an advanced skill IMHO, and the tuning parts are not as readily available as for other carbs.

The carb he's got is very adjustable and will work fine with some tuning...maybe we can wait for the OP to let us know the tuning steps they've taken to date and we can go from there

 

......however the "new" carters that no one seems to talk about are a vastly superior model to the afb's they sold the rights to edelbrock to.....we order them regularly in the past and there is a great difference starting with annular discharge......

 

I would suggest the carb you have. I am running the 770 SA on a 400 Pontiac and it is a very good performer. Please describe the symptoms (smells rich, smokes, accelerates slowly, etc.).

 

the problem I am having is a small miss under load, I pulled the plugs and they are running rich ( almost black around the tips). I have followed the adjustment in the holley manual.
1. I have set both the idle mixture screws so that I get the most vaccuum pressure. It is around 13.5
2. I adjusted the float level so that gas is barely coming out the site hole.
3.I am using the silver spring in the secondary

If I change out the plugs, the vette runs very well without any miss. Once the plugs start getting rich(black) I will then notice the miss under load again.

The carb seem easy to adjust. What am i missing.

 

You're not missing anything and you're off to a good start. This is a new carb, fresh out of the box, correct? Also, before starting any further tuning of the carb be sure your timing curve is right - MANY good threads on doing this. Always timing, then carb.

A primary jet change (and possibly a power valve change) is likely required and either a fuel-air meter (such as an Innovate) or some time with a pro tuner is suggested. The decision of how to proceed is based on how often you'll be tuning - either other cars or making significant changes to yours. If you're going to be doing this a bunch, investing in a good meter saves a ton of money over the long haul. You absolutely can do this yourself by just changing jet sizes until you're no longer coloring plugs - but it will ultimately take longer and may end up costing more. Holley produces a simple manual for making these changes and there are many other good resources on Holley tuning.

If it's a used carb, all bets are off. I've generally found that used carbs are typically way off, either becuase they were tuned for a specific engine very different than yours - or because they're selling it because they can't make it work....after changing everything. Start by restoring the carb to it's factory tune (jets, power valve, etc.) and work from there.

FWIW, I generally suggest adding $250-$300 to an overhaul budget for a tune. For a mild 350, many of the street carbs come with jetting that's pretty close - but step away from about 1 HP/CID or around 350 CID then the out-of-the-box setup isn't going to be right on...and a tune makes a HUGE difference in performance, driveability and fuel economy.

 

Without using a A/F meter, setting any type of carb is just an educated guess, about as accurate as setting the timing by ear.

Anyone that has ever used an a/f meter can attest to that and describe how far off a suppossedly tuned carb can be.

With that in mind, Holleys are extremely tuneable, and frankly quotes of poor mileage and poor performance come from the inexperienced, barely scratching the surface. In fact qjets are easier.

Seldom, have I seen Holley's set up properly to their fullest capability.

An investment in a A/F meter is a powerfull tool, no matter what type of carb you end up with, whether it be Qjets, Holleys, Demons, Webers, Dellortos, Mikunis or mechanical injection.

 

Thanks for the great advise, I believe that I may step down the primary jets by two until I see a difference in plug color. The power valve that is in the street avenger is an 8.5. Using the numbers in the Holley manual, it should be lower, 13.5 / 2 = 6.75. Would you recommend that I step down to a 7.0 power valve? Thanks

 

From the factory your carb was set up with 72s in the front, 75s in the back, and a 6.5 power valve. I would start with this set up and go from there. Then if needed - as a general rule - jet down until you notice a slight hesitation when lightly accelerating from a steady cruise in high gear (30 to 40 mph) then go up 2 sizes. The silver, or plain spring, is somewhat stiff. I would use the short yellow spring for your combo. Good luck.

 

Get rid of the 8.5 power valve, the engine is only having
to drop around 8.5 vacuum before the power enrichment valve opens you want the engine to have to drop vaccum as low as 6.5 before the power valve opens, more then a good chance with the 8.5 under to light of load its opening up dumping fuel in when your engine is not under load no need for it. vast majority of street holley carbs come with a 6.5 power valve.