Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Poor Fuel Mileage on 4.3 V6 with Quadrajet 17056250
bry593:
--- Quote from: don3194 on March 21, 2021, 08:52:29 PM ---I have attempted a vac gauge on it. Nice solid steady needle, no erratic movement.
--- End quote ---
Since you have blocked IABP, rebushed the throttle plate and still have high idle here are a few other suggestions:
Make sure your throttle stop tang is bent properly to allow full closure of the primary blades.
How many turns out are your idle screws?
What is your float measurement? Maximum 3/8 if no fuel regulator.
What size needle seat are you using? Maximum .135" for trouble-free daily driver.
--- Quote ---Whenever I lay into the throttle, enough to open the secondaries, I hear a weird rattling type sound. sounds like something in the carburetor is rattling.
--- End quote ---
Detonation usually has a tiny, pingy sound. Like bb's bouncing around in your cylinders. Heavy detonation can sound like a rattle. If you are using a Chinese distributor, most have no limit on the mechanical advance curve and advance well past 32 total. This will cause serious detonation. The solution is to limit the mechanical advance with heavier springs or a mechanical stop. Better yet, hit a swap meet and pick up a used GM distributor. The old HEI were well designed and usually only need lubricated, new weight bushings and lighter springs to wake 'em up.
bry593:
The float level listed above should be a minimum of 3/8. It will work fine between 3/8 and 7/16.
I bet it does drive a lot better if the power piston was never rising. That will cause a lean hesitation whenever leaving a stop light or during moderate acceleration. This assumes your throttle angle results in sub 8 in Hg. I noticed my truck leaves a light at about 10-6 in Hg. And when my spring was not lifting the piston, it hesitated and I had to flutter the throttle (add fuel with accelerator pump) to get it going.
Cliff Ruggles:
Hey all, I found the hole was NOT drilled in the baseplate.
Then it was from a turbo carb most likely
CCC carbs aren't drilled either, but they are slightly different in other areas like using a much thicker rod up to the accl pump arm, etc.
Your PP spring should NOT be a player for "normal" driving at light load. Heavy load or quick throttle movements yes. Any heavy or load applied quick enough to DROP vacuum below about 10" or so will also retard the timing as the VA will also come out of play.
I've logged many thousands of miles custom tuning with a vacuum gauge rigged up where I could see it and it's rare to see vacuum fall off much at all at vary light engine load. Most will actually be higher than they were at idle speed, unless you push down the throttle pretty quick and heavy. When this happens the accl pump is there to cover a momentary lean condition until the carb increases fuel delivery accordingly.......Cliff
don3194:
Just to put this part to rest right now, my PCV is not hooked up at all right now.
Its been a while but want to say I set my float level at 13/16" but again its been a month or so and I just cant remember for sure. I do have a fuel pressure regulator set to about 5-6 psi.
I dont know what size needle seat it is, Cliff sent it in a kit for a 17059222.
Where is the tang located, I mean having the carburetor off I can see that the blades close but I just want to check everything here. I can back the idle screw out until it is not touching.
I think my idle mixture screw are out in the range of 3-4 turns but I cant remember that either.
I also just want to say again that I remember when I first put this carburetor on, it had a good low idle and then something changed, a sucking sound started and the idle went up.
bry593:
If the idle screw can be backed out until not touching, that part of the equation is okay.
Idle mix screws at 3-4 is about right. So, nothing unusual there.
You are not blowing the needle off the seat and adding too much fuel if regulated to 6psi. So no problems in this area.
A sucking sound could be a problem. Another way to hunt down a vacuum leak is to take a length of vacuum tubing and hold one end to your ear while moving the other end around the carburetor base, manifold edges, etc.
If you had good low idle and then something changed, that had to be something you did. What did you change? Was this before the rebuild?
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