Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Stubborn Lean Idle Problem

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Cliff Ruggles:
.038" idle tubes would be plenty assuming stock engine with the original camshaft.

The 1971 455HO and 400 four speed carburetors are just too lean from the factory to work well on this new fuel. 

When you get time call me at the shop and I'll send a better jet/rod combo for it.  I've rebuilt and restored a lot of those and could never get one to pass testing with the stock tuning parts in it....

71silverstar:
Will do...Thanks Cliff and Kenth!

71silverstar:
Left a message at the shop...

Cliff Ruggles:
If I didn't call you back then I didn't get  the message.  Happens at times as calls coming in drown out the message that's being left, or I wasn't clear, etc....

71silverstar:
Sorry it took a while but I wanted to fill in the blanks on the final resolution.
As Cliff has said, most carburetor problems are actually ignition problems.
There was nothing wrong with the carb or the freshly rebuilt distributor either.
Cliff and Kenth suggested doing a cylinder pressure test just to make sure valves, rings, etc were not the culprit, so I bought a cylinder pressure tester and started removing the plugs.
Turns out, SOMEHOW, when I installed new plugs a while back, I managed to smash the electrodes down on 2 of the plugs so there was barely any gap and an obviously lousy spark.
I gapped every plug, was very careful putting them back in, and bam!  Fire breathing dragon!
And now, I have a solid 18+ inches of vacuum at curb idle, and the idle screws are responding.
I did replace the idle tubes with 0.038's.  I cracked the adjustable air bleed back off the stop about 1 turn as well.
It might be running a tad rich now, but that's just my nose telling me that after idling it back into the garage.
I can tweak a few things here and there now and see if I can really fine tune it, but it's going to be hard to improve on the performance right now.  It will spin the tires as originally designed, no problem.

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