I have a 68 400 engine it's stock with headers,performer intake and edelbrock 600 cfm carb. It runs great but I'm thinking of going with a bigger carb,is 750 to big? How about a 650? Im thinking the 600 is to small but I don't want to go to big and have it stumble and bog at wide open throttle. Thanks

 

My 68 400 had an Ebrock 750 on it when I bought it. I could never get it to run right. Bogs, hesitations, etc. I finally built a quadrajet for it, and it never ran better! So, I would discourage buying an Ebrock 750 for it, but I don't know about other brands (holley, etc)

 

There is an easy test to see if the carb is too small. Hook up at vacuum gauge (manifold vacuum) to it and see what it reads at WOT. It should be very close to zero. If it's over two or three inches I'd say the carb is too small and is a restriction. Depending on VE you're probably looking for something in the 680 cfm range.

 

I never could understand why somebody would take a motor that the factory put 750 cfm Q-jets on. Then expect a 600 cfm carb to perform just as good .

 

It originally came with 2 barrel carb! And summit recommended the 600 cfm with the performer intake. It's a low compression 400 that came with the 2 barrel I want to stick with a 4 barrel but the 600 is to small. Looking for some advice/help.

 

670 Street Avenger or 680 Quick Fuel. Either one would work well on that. And you can get a Performer intake and paint it to match the stock look.

Jmo.

 

How is the street avenger as far as adjusting and tuning?

 

On a low-compression 400, I'd think a well set-up Q-jet would be the best for all around driving!
Good MPG and ***** when opened-up!
68-69 442 carb would be good!!

 

You have to remember a Quadrajet is a variable cfm carb. Your going to get only what you you need up to 750 cfm. Quadrajets are also great economy carbs because the primaries are smaller than a comparable Rochester 2bbl giving a strong carb signal and great driveability. Assuming you keep your foot out of the secondaries.

 

What about an edelbrock 650? I already have the performer intake on the engine. Im not expecting neck snapping performance but just trying to get the most out of this engine. I'm thinking EBrock 650 or avenger 670.

 

You'll get various opinions obviously but I'd do the avenger or quick fuel. I hate edelbrock carbs, had 2, replaced them both with other brands.
Jmo.

 

Over the years my SBO wanted a larger carb compared to a similar SBC. A holley vac secondary 750 and later (with bigger cams) liked a double pumper 750.

 

you might consider the 3310 holley vac. secondary 750 or the edelbrock 750... a well tuned Q-jet is a great set up but due to the larger variety of jets, rods & hangers it isn't as simple to tune but of the 3 will give he best combination of power and economy. i've monkeyed with all three and love the holleys for simplicity and power potential but could'nt get the economy out of 'em like i could with the afbs... truthfully i have the least amount of experience with the Q-jet but for street manners and economy with great street performance the 'ol Q-jet is hard to beat.