Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Carb Starting point
77cruiser:
I run manifold vacuum on mine, I have it limited to about 10 deg. if I remember right.
BBvetteDRVR:
Still working on it but vacation is over.
piston is a little sticky in the bore so might not be pulling down, polished the bore and re-assembled so hopefully I can try sometime this week
M
Cliff Ruggles:
Yes, there is APT on that carb, it is located in the baseplate between the mixture screws. They can be stubborn to get loose, but if you can remove it we make an external APT screw for them.
Not sure why you are trying to employ so much mechanical timing with light distributor springs. I've NEVER had any luck with that deal using aftermarket kits. There is always some of the mechanical curve in at low rpms causing idle issues and huge drops in RPM's when the trans is placed in gear.......Cliff
BBvetteDRVR:
Ah, that (APT) it's been epoxied over
I switched back to a set of heavy springs on the mech advance to try to stabilize the idle more. Is slightly better but still seems to stutter. Drip seems much better but still there and the idle won't improve.
I've gone through the ignition wires with a meter and they seem fine but I'm going to pull the whole distributor and drop in another one and a set of wires to test.
The one in there is the original and other than shimming the end-play and new points/condenser/rotor and cap I've never really gone through it.
Hopefully if I can stabilize the idle it'll be enough to idle down that little bit more I think I need.
Cliff Ruggles:
NOTHING good happens with idle tuning until the ignition timing is rock solid and not adding any timing below about 900-1000 RPM's.
I fight this battle on a daily basis as a high percentage of folks looking for carb help also have distributor issues caused by well meaning attempts to establish a super-quick timing curve. For some reason that approach has been associated with "high performance" since way back in the 1970's when I first got into this hobby.
If you want sparkling throttle response and super quick engine power then choose the engine parameters wisely. Folks make poor choices, too much cam, LSA too tight, lowering compression for pump gas, etc, then find out their new engine idles poorly, soggy off idle and lacking in efficiency in the "normal" driving range. So they go after the timing curve to offset the negatives imposed from less than ideal engine parameters.
I've been seeing this for decades now, and not complaining, as it's brought a LOT of work in my direction!
Anyhow, keep working on the tune, I'm sure you'll get it nailed down.....Cliff
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