'70 Eldorado 500cid - Engine stalls instantly at full throttle
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  • 1 Post By deVille33
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500, 472, 425, 368 Discussion, '70 Eldorado 500cid - Engine stalls instantly at full throttle in Cadillac Engine Technical Discussion; Would there be an obvious cause for stalling at full throttle? I remember I had similar case fixed by an ...
  1. #1
    70eldo's Avatar
    70eldo is offline Cadillac Owners Connoisseur
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    '70 Eldorado 500cid - Engine stalls instantly at full throttle

    Would there be an obvious cause for stalling at full throttle?
    I remember I had similar case fixed by an engine shop that claimed a carb needle fell out and he glued it back in.
    If that would be the case again, what carb rebuilt kit would help me out?

    And if not, what other cause should I look into?

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    deVille33 is offline Cadillac Owners Connoisseur
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    Re: '70 Eldorado 500cid - Engine stalls instantly at full throttle

    Wow, that guy must have been good with the crazy glue. First thing - Do the secondaries start to open and do they open? There is a lock on the secondary that is temperature controlled, allowed to open after the engine is up to operating temperature and gets off the choke. Check the dashpots, see if they hold the proper vacuum.
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    Re: '70 Eldorado 500cid - Engine stalls instantly at full throttle

    The secondaries work. And the problem occurred just recently. Not gradually over time.
    What does that lock look like? I know under the kick-down switch (on the driver side of the carb) the spring rod (plastic) broke off. But full throttle worked before with that broken (since I bought it in 1999).

    About the vacuum: normally the air pump (for the level control) and the Carbon canister have a connection on top of the air filter. I presumed that was just to ensure filtered air. However, the connection of the air pump on top of the air filter broke off, so I just put a small (pneumatic system type) filter on that hose. Would this cause a loss of vacuum to the system causing this problem? If yes, when going after market air filter would I need to make a hose connection to the top of that filter again?

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    Re: '70 Eldorado 500cid - Engine stalls instantly at full throttle

    I checked the secondaries: they were fully open while not running. So I 'reset' the secondaries back into place with the choke lock. The choke brake itself seemed to work fine as in it could move in and out with noticable feel from the vacuum brake. Since the whole mechanism was a little sticky though I sprayed some lube on it.

    I also cleaned the whole carb with carb cleaner (while installed though; I have no time yet to do a whole rebuilt). I also cleaned the air cleaner and filter (K&N: with K&N cleaning kit and new oil).

    Since it was about midnight when I finished I will have to test it today. Tomorrow I will drive to a meeting in Sweden www.wheelsnwings.se

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    deVille33 is offline Cadillac Owners Connoisseur
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    Re: '70 Eldorado 500cid - Engine stalls instantly at full throttle

    If the secondary valve was open, it is a wonder the engine ran at all. The secondary operates like a second carb, and only operates when the draw from the engine exceeds the weighted value of the needles in the seats. This is called a demand system. Open the secondaries and look down the bowl. You will see where the needles are located and actuated by the valve. It sounds like a needle might have not set back down on it's seat. This should not have happened. Check to see if there is any foreign material down in the venturiis. Ensure the valve operates smoothly and drops back into place.
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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: '70 Eldorado 500cid - Engine stalls instantly at full throttle

    Make sure the secondary air door snaps shut because it is supposed to be spring loaded. I think you found your problem. The set screw must have come loose and lost the spring tension.
    The Ape Man and 70eldo like this.

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    Re: '70 Eldorado 500cid - Engine stalls instantly at full throttle

    Quote Originally Posted by cadillac_al View Post
    Make sure the secondary air door snaps shut because it is supposed to be spring loaded. I think you found your problem. The set screw must have come loose and lost the spring tension.
    Thank you all for the help so far!!!

    Is the vacuum brake supposed to 'suck' the secondaries shut, even when the engine is not running?
    Because that is what the vacuum brake is NOT doing right now; the secondaries will rest fully opened when the engine is off.
    Actually, when I push the linkage of the vacuum brake in it will spring back out when released.

    I found this on the secondary air valve spring:
    http://quadrajetparts.com/secondary-air-valve-spring-tensi-t-27.html
    I will have to do a small operation...

    If this helps, the part # of the carb is 7040230...

  9. #8
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    Re: '70 Eldorado 500cid - Engine stalls instantly at full throttle

    It took 3 exhausting late night sessions to rebuild the carb. I am very happy with the result. Initially I worried about the complexity of that project so I put a lot of preparation in it. But it turned out to be easy enough for me I could do it again with pleasure. I can't test it yet as I am still waiting for the new radiator. The old one I already took out...

    And I broke off the lever arm of the rotary downshift switch when I installed the carb back in. So I ordered a new one I found on ebay (at 2 am to give you an idea of when I have time to work on the car). I glued the original one with 2-component glue but I doubt that will hold.

    Also, I am amazed how nice (and fast!) the dremel can polish parts to high gloss! The throttle bracket and choke assy look like new now.

    Sorry, I have no pictures (yet).

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