Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: garybohannon on July 21, 2014, 08:24:40 AM

Title: Pig rich at wide open throtle (10.9-11.0 air fuel ratio)
Post by: garybohannon on July 21, 2014, 08:24:40 AM

My friends 1979 Trans Am 403 is rich at wot. The Fast meter shows 10.9-11.00 every time.
The engine has a 224-234 cam and ported heads and headers. AF ratios are 13.2 range at cruise. Idle is rich at 12.5-13.0.
Secondary air valve spring is "a little over half turn".
Au rods (.527 / long tips) and G hanger in secondary.
RobbMc fuel pump with 1/2" lines and pickup.
* My guess is that a metering rod with .30 tip would not cause that high ratio on the fuel.

Title: Re: Pig rich at wide open throtle (10.9-11.0 air fuel ratio)
Post by: garybohannon on July 21, 2014, 08:38:27 AM

Forgot to mention: Carb is an original 1979 Pontiac q-jet with Cliffs 2nd recipe.

Title: Re: Pig rich at wide open throtle (10.9-11.0 air fuel ratio)
Post by: Cliff Ruggles on July 31, 2014, 04:48:54 AM

It should be fine with .052" rods in it.  What primary jets and metering rods are being used?

Where is the float level?

Fuel pressure?

Diameter of the fuel inlet seat?.....Cliff

Title: Re: Pig rich at wide open throtle (10.9-11.0 air fuel ratio)
Post by: garybohannon on August 31, 2015, 07:45:17 AM

*  Fuel system has Robbmc pump, 1/2"fuel line, big filter.
*  n/s is .135"
*  Float is 1/4"
Secondary rods: swapped the .0527 for our new Ruggles custom .062 with G hanger, and got "Fast" meter reading of 12.0-12.2. at full throttle.
Primary jets: swapped .074 jets to .073 and still get 12.0-12.5 at idle, off idle and cruise.
 .....thinking we need to open the bypass a bit larger and lower the apt next. Can't see going to a .072 jet with ethanol-fuel and our 12 degrees initial advance.

Title: Re: Pig rich at wide open throtle (10.9-11.0 air fuel ratio)
Post by: Marx3 on September 01, 2015, 11:43:14 AM

I had a late 70's unit give me rich conditions no matter what I did. Found out the MAB's were too small. I opened up the upper mab's a bit ( can't remember from what size, to what size, but I would think I went up about .010 inches.
That cleared up any rich condition and the afr's were spot on.

What sizes are your MAB's?

Title: Re: Pig rich at wide open throtle (10.9-11.0 air fuel ratio)
Post by: Cliff Ruggles on September 02, 2015, 04:45:04 AM

Jet size has no effect on idle A/F.

APT is used to change part throttle A/F, and if you can't get it in range change to a different primary metering rod.

The 1979 403 used an Oldsmobile Q-jet, not a Pontiac q-jet, and they are similar but not the same and require a slightly different set-up when tuning them.

It would help to have ALL of the engine specs, and the carb number and exactly what's in it, and what tuning parts are being used, etc.....tks....Cliff