QJ accelerator pump trouble

Discussion in 'The Venerable Q-Jet' started by bw1339, Aug 25, 2020.

  1. bw1339

    bw1339 Well-Known Member

    I rebuilt the Quadra Jet (originally from a '68 Toronado) and now I have momentary bog in my 455 when accelerating hard. I checked the accelerator pump and I do get two streams, but only on the first 25-30% of plunger travel. After that, nothing.

    Any suggestions on what I may have done wrong? Thanks.
  2. knucklebusted

    knucklebusted Well-Known Member

    If it is bogging under initial load, check the rear air doors and the choke pull-off. The accelerator sounds like it is squirting.

    Check this. With the car off, if you press the rear air doors open, do they quickly return closed when you remove pressure?

    If the car is in park and the engine is running, how easy is it to push the rear air doors open? It should be very hard.
  3. hugger

    hugger Well-Known Member

    I don't run the pull off on Qjets,..unplug it ,..block it,. Set the rear doors where they have just a touch of psi on them,...

    From your wording it sounds as if it wasn't bogging b4,..but not much you could have done besides got the idle mixture wonky which will cause tip in hesitation
  4. techg8

    techg8 The BS GS

    Maybe the pump cup popped off and rode up the pump spring
  5. Stevem

    Stevem Well-Known Member

    Two things here, 1 many pump Pistons in kits these days are crap so I would order up one from Cliff Ruggles who post on this site, the other thing is that the pump check ball may not be seating on a good surface any more in the throttle body of the Carb due to crap or moisture corrosion which will made the pump action go back from where it came with the end result of running out of pump shot.
  6. bw1339

    bw1339 Well-Known Member

    I adjusted the accelerator pump arm and got a much longer shot. My bog reduced substantially.

    Looks like the stem was close to fully compressed in the rest position, so that it was close to the "overtravel" spring loaded range, which explains why I got a brief squirt at the start of the stroke. I will keep playing with it.

    Thank you all.
  7. Cliff R

    Cliff R Well-Known Member

    Do NOT remove, block off or disable the choke pull-off. It is there to unload the choke on a cold start and to prevent stumble/hesitation/bog going quickly to full throttle.

    The problem more times than not will be related to the choke pull-off. For at least 10 years now the white plastic pull-offs being sold for the pre-1975 carburetors are defective. They open WAY too quickly and allow the secondary air flaps to "whip" open causing a momentary lean condition. This requires winding the spring too tight to compensate and ruining it.

    I sell both "timed" and "adjustable" choke pull-offs for almost every model of Q-jet out there for this reason. I've been taking those white plastic pull-offs apart now for at least 10 years and modifying every single one I sell so they work correctly.

    I would also replace the plastic secondary cam and spring during any level of "rebuild" and why I supply them in my rebuild kits. The cam gets melted, worn down, and loose on the shaft. The spring gets tired as well. Correcting problems with secondary transition starts with these items........Cliff

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