Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Quadrajet leanning out at WOT

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73ss:
I have a very similar set-up. 489 stroker with Brodix Race rite heads. Chet Herbert HR cam with almost identical specs except its on a 114 LSA. 200 4-R trans with 2500 ish lockup converter and 3.73's in the rear. I have one O2 sensor & AFR gauge.

Carb is 17080212. (Factory BB truck carb) Cliff set me up with a kit. 76 jets & the custom 50M rods.
.140 N&S
.040 idle tubes (originals were .039)
.054 idle downs.
.135 bypass.
.090 idle ports.
In tank holley pump with external regulator set to 6.5 PSI. It holds 5 PSI during a WOT run.

In 4th gear with the convertor locked, 2200 RPM, 72 MPH I'm seeing 15.0~15.3. I can lean/richen this with the APT. Car seems to run best at this range. No surging or audible detonation and actually some decent fuel economy.

At WOT I was getting 11.9 ~ 12.1  I leaned it out with a rod change, It's approx 12.4 now. It does not slowly climb as you described.
(If you want exact rod specs I'll get them, My notes are in garage and I'm in for the night.)

I have not had any nozzle drip with this setup. I opened up the bypass to .135 to get it off the transfer slot. It's still on the transfer slot more than I would like but am hesitant to go any bigger on the bypass.

I'm curious as to what your main air bleed sizes are and if the carb is the single MAB type? Also, .063 idle downs seem big to me and .038 idle tube a tad small? I'm not an expert though.

One thing I did notice on the AFR is it goes pig rich after letting off of WOT. It did the same thing with a holley that I was playing with. I assume this is because of the high vacuum created and it's really pulling lots of fuel from the idle circuit? Has anyone else seen this with a AFR?

Cliff Ruggles:
"new needle and seat from Cliff's (I forgot the size and did not write it down but it is .130 or .135) "

It's probably .135" as I don't sell anything smaller than that.  Still not big enough for what you are doing.  I'd go to a .145" seat and make sure you have at least  7psi fuel pressure.....

Chris Goodrich:
Here is an update for those who are curious. I drilled the needle seat out to approx .145 (the closest drill bit size I had worked out to .142 something then I reamed it out a little bit with rolled-up sand paper before forming a new seat with an old check ball) and I went ahead and installed 77 primary jets while I was in there. It's not my air flaps that open to a full 90 degrees; I confused myself. It was my throttle blades that opened full 90; I actually opened the secondary air flaps further to get closer to 1.38 inches. Installed the engine, fuel system, and everything else. Took it out to seat the rings and made some WOT pulls afterwards.

I had the rev limiter on my ignition box set to 6,500 and hit that a few times without any of the breakup I was experiencing before. The engine starts right up with just one pump of the pedal before cranking. Idles on its own in gear at about 750 rpm in under a minute. Idles around 14:1, cruises, between 14 and 15:1. Stab the throttle and it spins the tires and takes off, no bog, no hesitation. Gets sideways, even from a 50mph roll. It was still pulling when it started to hit the rev limiter. Fuel pressure holds steady at 7.5 with the Aeromotive regulator right out of the box. WOT it runs around 12:1 AFR. I will play with the WOT AFR at the track to see what gives me the best ET and see if I can get the cruising AFR to lean out some as well. But I am pretty happy with it the way it is, runs great. It does go pig-rich, like 9:1- 10:1, immediately after coming off heavy throttle, but only for a few seconds. 

Cliff Ruggles:
Good news, and glad the fix was that simple....

77cruiser:
When you get to the track post some of your times & what the car setup is.

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