Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

weird off-idle hesitation

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Marx3:
Decided to grab the bull by the horns today and get this problem fixed.
It turned out that I did indeed need a softer PP spring.
drove around with a vacum gauge hooked up and it read 15-16 hg doing 50. ( on my cheap vacuum gauge anyways )
I figured my stock spring might be too stiff, causing the PP to be in the up position most of the time.

Anyways, I did some measuring and found a green spring to seem to push the PP up right below 14-15 hg. I installed it an tweaked the APT. Bye-bye off-idle hesitation.
Oh yeah, the car also got back it's ability to do a burnout :-)

It most certainly has been an educational day. Funny how you can read up on these things over and over again, but the troubleshooting dont seem to sink in as well, untill you actually deal with this IRL and fix it.

Cliff Ruggles:
Good news!

Marx3:
dang... decided to try a stiffer spring, since I felt the engine was not as crisp as it could be...
At the same time, I went from 70 to 71 jets, because I felt the 70's might have been on the smaller side...
Problem came RIGHT back.
Obviously I need to put back in the 70 jets and find the right spring again, but something puzzles me, that I wanted to run by you guys...
As of now ( with the 71 jets and 44 full tapered rods ) I get a nice tip-in result, with the APT raised about 3 turns. ( 50-80 rpm increase ). At that point the off-idle hesitation is quite noticeable. The car runs strong and you hardly notice when the pp-spring raises the pp and richen things up.

If I lower the APT ( for a higer rpm increase ), the off-idle response becomes less noticeable, but the car feels like it looses some torque and you can clearly feel the point where the PP jumps up ( torque comes back in )

I am starring myself blind on this situation...
What do you think of this?

Marx3:
70 jets installed, 150 rpm increase at tip-in: hesitation is gone again. :-)
Phew, that was educational :-)

Marx3:
although... at very light throttle, the engine tends to surge a bit, like it lacks power. Once I go into deliberate part throttle ( PP comes up ) the engine comes to life.
I mean, I can literally feel the engine needing fuel at light throttle, but if I raise the APT to bring in a bit more fuel, I get the hesitation RIGHT back...
What the heck does this tell me?
Idle system aint that rich, I think... 15hg at 800 rpm... Idle quality seems alright?

I have been testing a couple other Qjets, the last couple of days, and they all tended to have this light hesitation right off idle, Even though they have had slightly different calibration than the Qjet that causes this problem.

Could this be a simple case of too much cam and not enough converter and gearing?
I have 214/224@050 cam with stock converter and 2.41 gears.

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