Carburetor Tune Up Advice
 

I own a 1970 Chevy C-20 Pick up with a Rochester Quadrajet carburetor and need some help with tuning. The truck idles just fine, but when I try to accelerate relatively quickly the truck bogs down before shooting off. I've heard that these carburetors have a reputation for having that issue but I haven't been able to find a solution, only tutorials on how to adjust it during idle. What can I do to solve this problem?

Re: Carburetor Tune Up Advice
 

That sounds like the accelerator pump is malfunctioning or maladjusted.

When you open the throttle by hand while looking and listening down the carb (engine off) you should hear and/or see jets of gas spraying into the bores. If not, then you need to get a kit from the parts store that will contain a new little pump piston. You just take the top of the carb off and lift it out and replace it. The hard part might be getting the top back on with all the dangling needles and rods down into the correct locations but it can be easily learned how to get it right.

If you do hear/see spray, then maybe the setting is off. there are different holes that the connecting arm to this pump can be attached to. Very easy to set it to the inner hole for more spray.

Of course you should also make sure that you don't have a vacuum leak anywhere.

Re: Carburetor Tune Up Advice
 

Quadrajet Problems:
http://www.florida4x4.com/tech/quadr...20Problems.doc

Quadrajet Tuning:
http://www.corvettefaq.com/c3/QJetTuningPaper.doc

Quadrajet Choke Setup:
http://www.vetteclub.org/warehouse/t...ke%20Setup.doc

Bunch of Quadrajet links:
https://www.florida4x4.com/tech/quadrajet/

I agree with WorkinLonghorn, sounds like accelerator pump. The accelerator pump gives a spray of fuel to help with starting and quick throttle changes. If the accel pump is not working, you will have a hard time starting, and it will lean out momentarily when you increase throttle.

Re: Carburetor Tune Up Advice
 

The secondaries may also be opening too soon and that can cause a bog and sometimes a pop as well before it scoots off. Easy adjustment if you know what you are doing.

I would pull carb and get a rebuild kit to make sure the accell pump is fresh as well as no emulsion tubes are laying in the float bowl....

Re: Carburetor Tune Up Advice
 

On a lot of older/never rebuilt carbs, the accel pump seal gets chewed up pretty good by the ethanol and don't work real well.

Re: Carburetor Tune Up Advice
 

Sounds like a rebuild is in store as the others have stated. Here is some more tuning info on how to eliminate the quadra-bog when the secondaries open up.

https://www.dropbox.com/s/fhdxgp0wkn...s%202.pdf?dl=0

https://quadrajetpower.com/quadrajet-information/

Re: Carburetor Tune Up Advice
 

Just for motivation, as it’s been 10+ years since I last tuned a quadrajet, and can’t remember anything about them, once they’re tuned, they perform outstanding for their size. Plus they sound awesome!

Re: Carburetor Tune Up Advice
 

Something simple for you to check! My secondary’s were catching on the housing whilst in the closed position so check they move freely by pushing with your finger whilst the engine is off. Apparently the casings warp if 4 mounting bolts have been over tightened.