Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Chasing lean condition at WOT

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baxternick:
So my quadrajet has been great for normal every day driving around town. The engine is a healthy Cadillac 500 9-1. I installed a wideband gauge to monitor A/F ratio a few weeks back.  General driving around town is between 12.8-13.2.  Even moderate acceleration never is much above 13.3.  The issue I have is when I open up the throttle the ratio quickly climbs as I approach my shift point of 5200 rpm.  It is above 14.2 at times.  I have been trying to tune it out with different seconday rod and hanger combos.  All with crap results. 

The current setup is 75 Primary Jets, 50M primary rods, M hanger, and AX Rods. I tried a different hanger (G) and the car would have a huge bog even when secondary doors were tight.  I then tried the G hanger and some DA rods and all that did was cause a smaller bog and a VERY LEAN ratio.  I had to stop the pull at 4000 rpm. Am I wrong working on the secondary side?  Should I try some larger jets first on the primary side?  I was going to try a 76 jet with my 50m rods, but I didn't want to hurt current fuel MPG at cruise if I can help it.   

Thanks in advance for any help you provide!

Frank400:
What is the number on your Quadrajet and what was done to it ?  What mods have you done to the 500 (camshaft, intake, etc) .

    The numbers you are stating regarding around town cruising seem kind of rich to me.

 

Marx3:
Sounds rich to me too.
75 jets and 50 rods sound like the calibration of a large MAB's Chevy unit, but the AFR you see at city driving suggests otherwise. 
If I were you, I would get that sorted first.
 Know a 500 engine will need a lot of fuel at wot.
Did my buddy's Eldo once, and I couldn't believe it kept pinging, no matter how high I bent the hanger arms. It had gotten DA's too.

77cruiser:
It's probably running out of fuel at higher rpm. What size fuel inlet seat? How much fuel pressure?

baxternick:
The Carb Number is 17059206.  It is a larger MAB unit built by Jet Performance.  The engine is a 71 Model 500 30 over.  The cam is a MTS 15 Cam with Duration @ .050” range: 234, and Advertised duration range: 286-295.  I have a Edlebrock performer intake, and MTS shaft roller tip rockers. The car is a 54 Chevy that comes in at 3400lbs without me in it. The compression is 9-1.

 The car was having horrible bog issues over the summer which ended up being my fuel system starving for fuel with stock pump.  I installed a ROBBMC pump, and 8an line all the way to the tank.  Tank has 1/2" pickup as well.  That cured the problem for the most part.  I then decided to install a Innovate A/F gauge just to help with tuning.  I was alarmed to see the A/F climbing above 14 when the rpm climbed.  I actually kept a close eye on it today while driving to work and I was wrong in my cruise A/F ratios.  They are actually 13.2-13.5ish.  Once I crack it open a little to accelerate mildly they drop to 12.8-13.2.  Again these are 50M rods, so they have the larger tips.

  Fuel pressure seems to hover 4.5-4.8lbs around 4500RPM.  My needle and seat are .132" according to Jet when I asked them. The car starts and idles beautifully.  It has been a pleasure to drive on my daily commute.  Just alarming to see it leaning out when I do the occasional full throttle pull.

I currently have DA, CE, and AX Secondary Rods.  I also have B, G, U, and M hangers.  The factory carb that was cracked on my 500 when I purchased it was a  U Hanger, CE Rods, primary jet was a 74, and primary rod was 47B.

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