Caddy 500 Carb Questions
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500, 472, 425, 368 Discussion, Caddy 500 Carb Questions in Cadillac Engine Technical Discussion; I am not too familiar with carbuerators aside from my dirtbikes. Whenever i stomp on the gas the engine sputters ...
  1. #1
    MulishaPunk is offline Cadillac Owners Member
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    Caddy 500 Carb Questions

    I am not too familiar with carbuerators aside from my dirtbikes. Whenever i stomp on the gas the engine sputters a bit then kicks in, I assume this is due to the secondaries not opening fast enough. Is there a fix to this besides not givin it the gas. thanks
    '76 coupe deville

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    Katshot is offline Cadillac Owners Master
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    Re: Caddy 500 Carb Questions

    Could be just the opposite actually. If the secondaries dump too fast, the engine may sputter and bog. That's why there's a delay built into the secondaries. Beyond the secondaries, you might want to look at the accelerator pump, and ignition timing.

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    davesdeville's Avatar
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    Re: Caddy 500 Carb Questions

    First thing I'd check is the accelerator pump. Quickly, fully open throttle (as if you were flooring it) while you look down the primaries (front 2 barrels of the carb.) You should see a healthy spray of gas. If not it's time to replace the acc. pump.

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    Aaron J Williams's Avatar
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    Re: Caddy 500 Carb Questions

    Also, quadrajets have a brass power valve which sticks and causes the same symptom. If the secondaries are opening too fast there is a little clockspring on the shaft which can be tightened . On the passenger side of the carb by the secondary air valve there is a real small allen head secrew and directly above it is a flathead screw which the little spring is wound around. Back off the allen head screw and turn the flat screw to adjust the tension. There is also a vacuum break which slows the secondaries from opening too fast. That can be adjusted by bending the link between the vacuum can and secondary air valve. Make sure that can holds vacuum also.

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    Re: Caddy 500 Carb Questions

    I am having what I think is the same problem with my El Dorado (same engine setup) When I punch the gas, it will sputter and stall, then kick in when I let off. IF I really floor it as if to burn out, the engine will sometimes die. I know almost nothing about carbs, so if anyone could point me out to waht to adjust/what you guys are talking about, that would be great.

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    Re: Caddy 500 Carb Questions

    first check the accelerator pump like Dave said.

    Then, adjust the secondary air door spring tension. Heck - do this anyways, it is about the best thing to do on a Q-jet. Scroll about half down this page: http://www.73-87.com/7387garage/drivetrain/myqjet.htm

    Unless you have modified your engine, I wouldn't do anything they mention on the page about changing the rods and hangars - GM tuned the fuel curve pretty well from the factory.

    Also check the secondary air valve dampner - the little vacuum cannister on the passengers front of the carb that has a little metal rod going back to the secondaries. With the engine off, gently push the rod all the way into the cannister, then let go and time how long it takes to let all the way back out. Less than 1 second and it needs replacing. As long as 2-3 seconds is acceptable. Longer than that and you probably have a blockage somewhere - either clean or replace.

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    Re: Caddy 500 Carb Questions

    Alright, then today I will check teh acc. pump (by making sure there is a nice spray of fuel when I look down teh primaries, right?) and I'll adjust the door spring tension, and finally check teh valve dampener...about the dampener...so 2-3 seconds is teh sweet spot? As in if it comes out too fast or too slow, I'm in trouble, right?

    Thanks again guys, sorry I'm such a noobie, but I guess you gotta start somewhere.

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    terrible one's Avatar
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    Re: Caddy 500 Carb Questions

    Didn't get to check teh acc. pump today, on teh account of the fact I was working alone. Checked that vacuum cannister, got to teh 2nd second just before it came all the way back out. Bout time for a replacement?

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    Re: Caddy 500 Carb Questions

    2 seconds is fine. For a performance engine, 1 second or a bit longer is better, but two is great if your engine is mostly stock.
    The thing is, a slow-opening air door wouldn't cause the engine to stall and die, it would just cause hesisitation when you first floor it. Too fast opening would cause stalling.

    You can check the accelerator pump yourself - the throttle linkage connects to the drivers side of the carb. It is either a long metal rod or a cable. Hold the choke flap open, grab the throttle linkage, and give it a twist.

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    terrible one's Avatar
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    Re: Caddy 500 Carb Questions

    I'm pretty sure I know what ylu are talking about when you say throttle linkage...mine consists of a chain thing (made of those little balls, i think) that attaches to the driver side of the carb. It has a lot of slack in it. This it? This normal?

    When I hold hte choke flap open and grab the linkage and "give it a twist" are you referring to the choke flap or what? Sorry, but I'm still very unknowledgeable.

    Thanks

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    Re: Caddy 500 Carb Questions

    the chain thing is the cruise controll - that connects to a vacuum diaphragm that controlls throttle position.
    The throttle linkage to the pedal attaches to that same bracket that the chain comes to. Although, pulling on the chain would produce the same effect of opening the throttle.
    Give the throttle a twist while holding the choke flap open (so you can see in)

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    Re: Caddy 500 Carb Questions

    Ah I see. Well, my cruise control doesn't work. I'm not sure if it is electrical or the chain thing. It has tons of slack in it, for one.

    Also, the choke flap...is that the big butterfly or the little one? Hehe...I feel stupid asking that.

    But so pull the chain to open up the throttle, and then hold the choke flap (probably the one not already open by me giving it gas). This will allow me to check and see about a nice, healthy spray of gas being provided by the acc. pump, right?

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    Re: Caddy 500 Carb Questions

    The choke flap is on the primaries (the smaller barrels on the front side of the carb.) The secondary air doors are the valves on the top of the secondaries.

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    Re: Caddy 500 Carb Questions

    Alright, will check today. Is it normal/okay for it to have a load of slack in it? At one point it is touching the engine (intake manifold). So it has a lot of slack.

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    Re: Caddy 500 Carb Questions

    open the choke door first, but you've got the idea.

    That seems like alot of slack on the cruise. Mine has just a touch of slack so it doesn't hold the throttle open at idle, nothing more. If the vacuum diaphragm can't pull it in far enough, that could be why your cruise doesn't work.
    If you turn the cruise on, and try to set it, does the green 'cruise' light come on? My set button is finicky - only works with just the slightest nudge. Push it all the way in and it doesn't do anything. You can also check the diaphragm by sucking on the vacuum line going to it.

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