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Thread: Will not Idle after Full Throttle

  1. #1
    74corvette Guest

    Default Will not Idle after Full Throttle

    Hi there, I have been running a model 4160, 750CFM vacuum secondary, electric choke holley carb for 4-5 years now. I have the carb tuned well, plenty of power and good throttle response, etc.. The problem I am facing is the engine will not idle after I open up the throttle and allow the secondary’s to open up. As long as I never go full throttle my engine will idle perfect. Also, after I go full throttle and the engine will not idle, to get the engine to idle correctly again I must turn the engine off, only for a couple seconds, re-start and idle is back to perfect again. This issue is not intermit, it is every time I go full throttle without fail. If anyone has any ideas on what I can do to fix this I would appreciate it.

  2. #2
    rickyr Guest

    Default carb

    it sounds like the connecting link from the pri. to the sec. linkage might be bent
    and not closing the sec. plates right
    the part # of that link is 20-53
    I would try replaceing it

  3. #3
    74corvette Guest


    I had suspected that the secondary’s were not closing all the way back, so I did try to close them by turning the lever with my hands, with the engine running in the bad idle. It didn’t do anything, I even covered up the secondardy side of the carb to see if that would make a difference, it did not. I will take a closer look at the secondary linkage this weekend, just in case. Is there anyother possbile fix’s for this? One thing I fogot to add in my first post was, when the engine is idleing proper the exaust has a normal smell, but when the engine will not idle, the exaust has an unburnt gas/fuel smell.
    Thanks again for your response.

  4. #4
    rickyr Guest

    Default carb

    Do you have the right size power valve for your vacuum reading?
    the power valve needs to be 1/2 of what your vacuum is at idle (in gear if auto trans)

  5. #5
    74corvette Guest


    Thanks for the help & suggestions, turns out it was the power valve. I had a 6.5 in.Hg, for a vacuum of +-10 in.Hg at idle, which worked well for years. Using your suggestion of half the vacuum, I gave a 4.5 in.Hg power valve a try, and that was it, back to idling perfect. As a side question, can power valves change their opening vacuum levels after some time, ie springs or rubber get softer or harder over time or something? I am just curious because the 6.5 inHg power valve worked well for years, why would things have changed? Thanks again.

  6. #6
    rickyr Guest

    Default power valve

    I have never heard of the vacuum rating changing on a PV

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