Am I missing a part, or two?

Discussion in 'The Venerable Q-Jet' started by MikeCasey, Aug 12, 2023.

  1. MikeCasey

    MikeCasey Well-Known Member

    I'm sorting out a '68 GS400 convertible formerly owned by @efogs400. It wasn't taken care of by owners between he and I, but that's a bar room conversation.

    The car won't run without me on the gas for a minute or so, then idles @ 700, then idles at 1000-1100 after driving it. I've gone through timing, and carb mixture settings, but found the choke not hooked up. Overall, the car drives good. I'm just trying to sort out the high idle & lack of kick down, which it doesn't.

    The spring is in the manifold, but when I connected it the way I think it should go, the flap closes and won't return to the open position. I also think I'm missing at least a screw (!?!?!? I know ... LAYUP !?!?!?!?) and maybe something else.

    Here are a couple photos. Hopefully a QJ guru can tell me... I've never dug into carbs that much.

    Thanks, in advance, for your help. 68 QJ choke side 1.jpg 68 QJ choke side 2.jpg choke spring.jpg
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The choke thermostatic springs get tired after many years. That is one possibility. The other is the exhaust cross over passages in the heads/intake may have been blocked off. That mod keeps the intake cooler for better performance, but the choke thermostat doesn't receive the heat it needs to open the choke. The answer to that is to use an electric choke kit.

    If the choke is even partially on, it will hike the idle speed a bit. Could also be a weak throttle return spring, or sticky throttle blades. Another possibility is light distributor springs that bring in some mechanical advance at idle speeds.

    The kick down for the THM400 is electrical. Pretty simple to diagnose. There is a switch under the dash operated by the gas pedal. It passes 12 volts down to the transmission case connector and operates a solenoid inside the pan. If you apply 12 volts directly to the transmission, you should hear the solenoid click. If you do, check the gas pedal switch to see if it works and is connected. Then check the wiring for continuity between the gas pedal and transmission.

    Hope that helps.
    Last edited: Aug 14, 2023
  3. MikeCasey

    MikeCasey Well-Known Member

    Thanks for your reply. I’ll look into an electric choke. My car is a 3-speed manual.

    I can ask the shop that just built my motor about the heat passages.
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    OK:) Your original post mentioned lack of kick down.:)
  5. MikeCasey

    MikeCasey Well-Known Member

    Yes. When I come to a stop the idle stays around 1,000-1,100. I give the throttle a good blip and it drops to 700, and sometimes a snitch lower.

Share This Page