ok this is for my brothers 77 vette with the l48 and automatic trans... he just got done rebuilding the carb... and we need to know the setting for the air and fuel screws on the front of the carb... also how do we set the rest of the card to factory or what ever is good for performance... who ever had it before was an iditot it ran like **** right now it idesl ok but it bogs off the line when you get on it and acts like it has no guts what should we do to get the power back...also should a 77 vette with auto be abel to spin the tires....? mods soon to come in a few weeks are headers full exahust and intake...thanks for any help ...

 

Idle mixture screws will not affect overall performance of the carb. If you have a stumble and other problems, there are issues with the carb setup that are not related to external adjustments.

Base setting for the idle mixture screws is 4 turns out from lightly seated. But this needs to be adjusted and set up for the car/engine combo. Acceptable range is between 2 to 6 turns.

A base 77 auto trans Vette will have trouble spinning the tires out from a standing start on dry pavement with the stock rear gears.

If you're going to add headers, you will need to re-jet that carb.

Contact me if you need the carb set up right:
V8FastCars@msn.com
Lars

 

sent e-mial to you for help if anyone elses would like to help please post ways to help set this carb up right thank you...

 

Lars is all you need for the right fix!!

 

To set idle, I use a vacuum guage connected to the manifold vacuum get the highest reading at idle then adjust back down 1/8 of a turn on the mixture screws. Here is some info:

http://www.centuryperformance.com/vacuum.asp

First make sure that your timing is correct. See sticky at the top by Barry K.

Oh, BTW, I would take Lars up on his offer to help with sorting out your carb problems...he knows what he is talking about.

 

But what about those people who claim their "stock" cars will lightem up and "chirp" the tires when shifting to second?

 

L82 with really skinny tires with 50psi and a 4:11

 

Yeah... it's called "power braking." I can smoke the tires on a 75 Caprice station wagon the same way...

Not sure what you're looking for in terms of setup advice. The carb needs a precision rebuild - you cannot simply "put a kit" into a Q-Jet and assume it will run well. All the previous errors of all previous builders need to be identified and corrected. Most Q-Jets have defective and altered parts in them, and these need to be removed and replaced. Jetting needs to be corrected back to the stock baseline and modified from there if justified by the engine needs. It is not possible to have a Q-Jet run well by simply "rebuilding" it. Right now, I have 3 Forum-member Q-Jets on my work bench, and all of them look like they're just fine. Here are the problems I found with the carbs:

Carb 1:
Incorrect primary jets
Incorrect primary metering rods
Incorrect secondary metering rods
Missing APT assembly
Missing inlet spring
Ruptured pulloff
Incorrectly set secondary AV spring
Incorrect power piston spring
Power piston hanger arms set at incorrect angle
Secondary throttle linkage bent and incorrectly adjusted

Carb 2:
Secondary metering rods incorrectly installed, jamming AV
Emulsion tubes fallen out of airhorn and incorrectly installed in wrong place in carb
Incorrectly set APT
Incorrect pulloff
Float clip incorrectly installed, jamming float

Carb 3:
Porosity in bowl casting causing uncontrollable idle circuit
Incorrect idle mixture screws installed
Bowl filler missing
Secondary rod hanger bent to wrong height
Missing fast idle cam
Warped airhorn causing air leak into primary metering circuit

On any 3 of these carbs, if you had simply cleaned the carb up, installed a kit, and put it back together the way it came apart, the carb would be a mess and never run right. This is the norm with Q-Jets due to their age. There is no secret setup procedure on the carbs: You have to identify the problems, replace or repair all the problem parts, set up to spec, and the carb will run right. If the carb is not running right, or if you have a bog, the carb has not been set up to its spec, and you have not fixed the problems in the carb.