Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Rich at WOT, lean at idle and cruise
77cruiser:
13.5 for idle is good but if you can get a better idle by adjusting the mixture screws don't pay attention to AFR at idle. Lower the primary needles a bit more to lean the cruise.
Try loosening the air spring just a bit more & that rich transition should go away.
Cliff Ruggles:
I would get one of our SR rebuild kits, it will have everything required for a complete/correct rebuild including a new secondary cam/spring, complete accl pump assembly with new springs, float, and a high float N/S assembly.
That carb should have the large MAB's and should be showing much leaner at part throttle or at least more control with the APT system.
Assuming you are running vacuum advance light throttle A/F should be leaner at very light load.
8 turns out with the mixture screws and .093" holes under them indicates you need to open up the idle tubes and DCR's for what you are doing. Keeping in mind that idle fuel feeds the main system as well and is the first thing to nail down when tuning, then move on to the jets, metering rods, and APT adjustment........Cliff
modrummer:
--- Quote from: 77cruiser on June 04, 2018, 07:23:29 PM ---13.5 for idle is good but if you can get a better idle by adjusting the mixture screws don't pay attention to AFR at idle. Lower the primary needles a bit more to lean the cruise.
Try loosening the air spring just a bit more & that rich transition should go away.
--- End quote ---
Lowered the primary needles with the APT screw and loosened the air door spring tension another quarter turn. Some slight improvement for sure. I"m getting closer, it's pretty much fine tuning at this point.
One issue I'd like to figure out is the smell I get at idle. Part of it is that I'm running a carbureted vehicle with no catylytic converter, but I've run vehicles like that before and they didn't smell this bad. So I'm wondering if I have the PCV hoses hooked to the wrong ports, or some other vent port plugged that shouldn't be or something.
See attached pictures. The big hose circled in red goes to a T fitting with one end going to the PCV valve in the valve cover and the other end going to the charcoal cannister. The hose circled in green goes straight to the charcoal cannister. Is this correct?
And then in the rest of the pictures you can see the various ports that are plugged off. I am running full manifold vacuum for the vacuum advance.
Also, what is the port circled in blue on the back of the carb near the secondary air doors? Just another vacuum port?
modrummer:
--- Quote from: Cliff Ruggles on June 06, 2018, 04:40:11 AM ---I would get one of our SR rebuild kits, it will have everything required for a complete/correct rebuild including a new secondary cam/spring, complete accl pump assembly with new springs, float, and a high float N/S assembly.
That carb should have the large MAB's and should be showing much leaner at part throttle or at least more control with the APT system.
Assuming you are running vacuum advance light throttle A/F should be leaner at very light load.
8 turns out with the mixture screws and .093" holes under them indicates you need to open up the idle tubes and DCR's for what you are doing. Keeping in mind that idle fuel feeds the main system as well and is the first thing to nail down when tuning, then move on to the jets, metering rods, and APT adjustment........Cliff
--- End quote ---
Cliff,
I just ordered one of your SR Rebuild kits. I am running full manifold vacuum for my vac advance since my engine runs better with it. Tried hooking it up to ported advance and it ran very rich at idle and the mix screws did nothing (could screw them all the way in without killing the engine).
I have 18 degrees initial timing, 18 mechanical (36 total) and 20 degrees of vac advance. So I get about 38 degrees of timing at idle with the vac advance hooked to manifold vacuum. Is this too much even though my engine seems to like the extra timing?
Cliff Ruggles:
Open up the idle tubes and DCR's and go back to ported vacuum for the advance. It's simply WAY too lean at idle if you need to run 18 initial plus 15-20 more degrees from the vacuum advance.
I see this a lot with aftermarket camshafts as they have more overlap and degrade vacuum at idle (signal) to the carburetor and the carb was originally calibrated for a "stock" engine making at least 20" vacuum at idle speed.
Everything will get better once you modify the idle system......Cliff
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