Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Quadrajet Off Idle Stumble

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Shady Tree Garage:
Just finished a rebuild on 17080213 carb on my 1984 K2500 350.  Clean as a whistle now thanks to Ethan's suggestion to soda blast.  Jetted 72/50 per oem spec, apt measured and set with caliper and seated at idle, manifold vac approx. 17-18 with a "8" spring under power piston, starts to pull up around 6-7 inches actually.  Set accel pump rod height according to spec sheet (9/32), but I notice that the pump rod doesn't even start to move until throttle plates have opened a few degrees.  Coinciding with this, as I come off idle, at first smooth then (I believe just as pump begins to actuate) stumbles, worse when cold.  Once engine is warm, if I "feather" the accelerator, I can get past the stumble, but it seems like the pump shot causes the stumble!?  Mixture screws have little affect except on vacuum and even turned all the way in don't kill the engine.  Checked and re-checked my adjustments on most everything I can think of.  Idle and cruise are smooth and beautiful otherwise.  Big question bugging me is should there be movement of the throttle plates of a few degrees before the movement of the accel pump rod and linkage? Thanks in advance for your thoughts!   

429bbf:
shady something doesn't sound right . you should have to push the acc. pump down a little to get the pin in on the pump lever . there should be no gap . do you have the right return spring under the acc.pump?did you test for leakage if the ball was seating properly?what you are explaining would cause your problem no added fuel from the acc.pump when you start to open the throttle plates will cause a big stumble. fwiw

Shady Tree Garage:
Thanks for the info 429bbf.  There is no gap between the pump lever and the piston and the ball appears to be seating with no leaking.. I get a good pump shot when the linkage pushes up but the throttle linkage opens a bit before the "cam" that is attached to the pump linkage begins to move and push the linkage up.  The throttle and the "cam" that pushes the pump linkage up are on the same shaft (throttle shaft), but they move separately with the cam delayed by a few degrees and I can't see where the mechanism intersects at the point of movement.  The choke apparatus blocks my view of the throttle on the passenger side.  Do you know if there is a tang (perhaps on the passenger side out of sight) that needs adjustment so both move simultaneously?  Hoping to avoid removing carb again unless I know what I am looking for.  Thanks again for the help!

429bbf:
there can only be a couple of problem. ether the tang (the piece that the acc rod attaches to is loose on the throttle shaft)or your holes are worn out,or your rod ends are worn out. the piece on the throttle shaft should be solid . no moment. where are you hooked to the bell crank ?inside or out . inside gives more pump shot.fwiw

Shady Tree Garage:
Thanks again!  That sounds like the likely problem then.  The rod is connected to the inside hole.  If the tang that the lower end of the rod is attached to is supposed to be solid with the throttle shaft, that is where the problem lies, because it is not.  Not sure what the fix is, but now I know where to work.  Thank you very much.... I will report back when I figure out a solution.

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