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Electric choke won't open all the way.

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  • Electric choke won't open all the way.

    I have a 670 Ultra Street Avenger with electric choke installed on a new HT383 from Chevy. I also have a TPS kit (Holley 534-202) installed on the carb. Truck fires right up and the choke does what it is supposed to do until its time to let go of the last notch of fast idle. It just will not let go of it. I can let it idle for as long as you want and blip or hold the throttle and it will only settle down to the last step of fast idle, approx. 1050 RPM. If I actually push down on the red fast idle cam, if will then release and go to hot idle of 650 RPM, but it will not do it without pushing down on the red fast idle cam. I can see the fast idle lever and it has free range of motion, neither it nor the fast idle screw are rubbing against anything. I'm pretty certain the hang-up must have something to do with the TPS bracket, but I'm not sure and I have a bunch of questions, maybe someone can help.

    While at 1050 and the choke plates are not vertical I can push it towards the windshield and they return to not vertical with a spring action which makes be believe the choke just isn't ready to open it all the way yet, but how long does it take for that to occur? 3, 5 10 minutes?

    On an electric choke, does the opening of the choke plates occur solely based on the amount of time 12 volts are being applied to the bi-metal spring? If this is correct then the actual temperature of the engine has nothing to do with the choke being fully open, right?

    When you "set the choke" by depressing the throttle before initial start-up, should the choke plates be fully closed or just slightly open? When the choke is working towards being fully open, does it actually hold the throttle open with the fast idle cam? or does the increase in RPM come solely from the change in fuel/air mixture being created with partially closed choke plates? So that's my situation and a few of my questions, any help would be greatly appreciated. Picture is as far as choke wants to open on its own.
    Click image for larger version

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  • #2
    The choke should close all the way or nearly all the way with a cold engine, and within 3-5 minutes of turning on the ignition (depending on how it's wired) it should be all the way open. It's 100% dependent on being supplied +12V to the choke heater, independent of engine temp. The older design chokes used hot air system that was dependent on engine temp to open the choke, these would not open all the way till the engine warmed up. Normally these opened slower than an electric choke. Fast idle cam is what raises your cold idle speed when the choke is not fully open. If it doesn't fully open you will have the problem you have, that's the idle won't return to curb idle.
    These are adjustable, if you loosen the three screws that hold the clamp on that circular black choke heater cover you can turn it so that it opens all the way when the choke heater is hot. Be careful that heater and the black cap gets hot.
    In the picture, I'm not sure if that TPS may be causing it to not open all the way, I've never played around with one of those on a carbed engine. So turn on the ignition or run the engine if you have to in order to make the choke open and then loosen those screws and set it so it just opens all the way. It's a compromise really between fully opening and fully closing. Even if not all the way closed when cold, it will usually start fine because the choke unloader or vacuum break as it's also called has to pull the choke plate open a fraction of an inch to keep the engine running after a cold start.
    As an aside, the best way to wire up one of these chokes is to a source that has +12V only when the engine is running, if you have it wired to a source that gets power whenever the ignition is on, but before the engine starts, the choke will often open too fast.
    Last edited by Lou C; 04-10-2022, 12:31 PM.

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    • #3
      Thanks for the response Lou C. I do have the choke wired to only have power on accessory or ignition so I can try to just turn the key and wait, then adjust the choke to see if it ever opens all the way, then retighten. That's a good idea. It just seems to be hanging on something. Knowing I can fool with it without it running and burning myself on the headers really helps. I have the wheelwell out so I can stand in the engine bay, but getting to the bottom of those three screws is not easy with the TPS bracket in the way.

      If it still seems to be hanging on something no matter where the choke is, I'm gonna have to take the TPS off and try and do the process of setting the choke properly without TPS and see if that works. Then just move forward one part at a time.

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      • #4
        UPDATE: I tried the process of powering the choke without the engine running. The choke opened all the way and did it within about three minutes so there's NO hangup in the actual choke linkage. When doing so, the Red fast idle cam (RFIC) stayed all the way up and didn't interfere with the connection rod between the choke and the choke plates. When I pushed down on the RFIC with the choke all the way opened, it immediately dropped all the way to the bottom where it's supposed to be. So the hang up occurs with the process of, as the engine is running, the throttle adjustments being done as the RFIC drops down from fast idle to intermediate to curb idle.

        I called Holley with this information and was told that 99% of the time this problem is due to the fast idle screw hanging up where it connects and rubs on the RFIC. The fix is to adjust the fast idle screw out until the issue goes away.

        So that's where I am now. To get a true test though the engine has to be fully cooled to ambient temperature so I'm turning the fast idle screw about a quarter turn a day until this problem goes away.

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