Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Edel 1901, AMS out, Still Lean at Idle
bry593:
Q. Are you using the APT system in the baseplate? We install an external screw at that location so we can fine tune part throttle A/F without taking the carb apart and changing metering rods.
A. Yes, I got a new APT screw and spring from you. I have tuned it with the tip in (+50ish rpm @ 2000), but I've noticed my gas mileage has dropped a bit. I'm thinking about changing from the .035" to the .045" primary rods with the #69 jets per your original recommendation. On a side note, the choke works great, starts right up and begins to roughen up after 30s, hit the pedal once to drop it to the next stop and it idles clears up. At that point, I'm hitting the rouad and the choke is completely off. Works better than any quad choke I've had.
Q. The .125" N/S assembly is too small for the power level and .420" is too low for the float setting unless you have a high pressure fuel pump w/o a regulator.....Cliff
A. I drilled the seat out to .125" per recipe one. You think I should go larger? This isn't really a high-power car, just a large engine in a relatively heavy, 1970 Caprice. I have the float set at .313", not .420". I chose this as a compromise between your and Lars recommendations. Seems to be working okay, and there are no gas fumes or soaked airhorn gasket issues.
At this point I have a few other projects to tidy up (motorcycle fuel system overhaul, front rotors for the Caprice, painting the house, etc.). Might be awhile before I can provide further updates as I dial it in for peak efficiency.
Cliff Ruggles:
Since you have APT install the larger metering rods, the smaller ones will not provide full control of A/F from rich to lean.
Install the high flow .135" N/S assembly and set the float to 1/4".
Fuel level effects the calibration, and the float level and fuel seat diameter effect the fuel level. Unless the fuel pump is really high pressure, there is no need to run a low float setting......Cliff
bry593:
Will do. Won't take too much time to pull the carb off and drill and peen the needle jet, bend the the nitrophyl and swap out the primary rods. I'm getting pretty speedy at this point.
Should I change out the DR secondary rods to DA? The DA are a bit smaller, but have a longer tip. If so, can you explain how this would benefit? I'm not sure I understand the theory behind the medium and long tips.
Cliff Ruggles:
They will richen up the A/F at full throttle, probably a good move, DR's have a much larger tip and leaner. I always prefer a little extra fuel at full throttle, keeps the rod bearings out of the oil pan in most cases!.....Cliff
bry593:
I swapped out the rods for the .045, reset the float to 1/4", but did not drill out the needle jet (was in a hurry). Set the IMS to 2.25 turns out and readjusted the APT at 2000 rpm.
Loaded up the family, filled up with gas and then drove 65 miles to another gas station. Refilling the tank to the same level (all the way up the fill hose) took 2.4 gallons. 65/2.4 = 27 mpg at 70-80 mph. That's with a TH400 and 2.56 gears. I'm going to finish out this tank to see what my average is with in town driving.
Cliff, I'd say this carb seems dialed in.
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