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Thread: Low engine vacuum but no vacuum leaks.
          
   
   

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  1. #1
    47Fordcoupe's Avatar
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    Low engine vacuum but no vacuum leaks.

     



    Hello everyone, I'm new here.. hoping someone could help me figure this out. So I recently purchased this car which has a 305 SBC in it. The engine starts right up when cold, but hard to start when hot. I already ruled out vapor lock as well as engine vacuum leaks. My vacuum gauge is fluctuating between 5" Hg an 7"Hg.
    Also my timing seems to be way advanced at 30* at idle and I can't bring it down without the engine stalling.. I did find tdc and checked harmonic balancer mark. Thanks in advance for your inputs.
    Last edited by 47Fordcoupe; 07-26-2018 at 09:04 PM.

  2. #2
    firebird77clone's Avatar
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    Possible:
    Harmonic balancer ring slip.
    Engine not degreed upon assembly
    Vapor lock( you sure? Pop the hood about three minutes after shut down, LOOK down the carb bor, see if fuel is dripping down)
    .
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    What size are the battery cables and are the grounds clean and tight? If it fires right up after it cools off it can be a number of things including a bad starter and/or solenoid. and as mentioned it could be a fuel issue, but I would check the grounds first and where is the battery located?
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  4. #4
    47Fordcoupe's Avatar
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    Quote Originally Posted by firebird77clone View Post
    Possible:
    Harmonic balancer ring slip.
    Engine not degreed upon assembly
    Vapor lock( you sure? Pop the hood about three minutes after shut down, LOOK down the carb bor, see if fuel is dripping down)
    Thanks for the reply. I already ruled out a harmonic balancer ring slip. Found tdc with a piston stop and made a new mark on the balancer. Installed a 1" wood carb spacer, , heat shielded the starter and solenoid, fuel pump and fuel line, installed new spark plugs/wires, new distributor rotor,coil and cap. Idle timing is set at 30* and it won't decrease without stalling.

  5. #5
    47Fordcoupe's Avatar
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    Quote Originally Posted by NTFDAY View Post
    What size are the battery cables and are the grounds clean and tight? If it fires right up after it cools off it can be a number of things including a bad starter and/or solenoid. and as mentioned it could be a fuel issue, but I would check the grounds first and where is the battery located?
    Battery is in the trunk and cables and terminals are new and clean. This is not a fuel issue. As I mentioned, the vacuum is very low as if there was a leak...but there is no vacuum leak. Thanks

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    So I recently purchased this car which has a 305 SBC in it.

    The engine starts right up when cold, but hard to start when hot.

    My vacuum gauge is fluctuating between 5" Hg an 7"Hg.

    Also my timing seems to be way advanced at 30* at idle and I can't bring it down without the engine stalling..

    You said this at first... I did find tdc and checked harmonic balancer mark.

    Then, on your last reply, you said... Found tdc with a piston stop and made a new mark on the balancer. Installed a 1" wood carb spacer...

    By you saying everything checks out A OK, you are fine, and have no troubles at all.

    I say, you are a tooth off on the timing gears, or the chain is so sloppy, it will fall off soon... OR, you do have a vacuum leak, and your not finding it. Does it have a PCV ? Cracked vacuum hose ? Cracked Wood Block ? Are you Checking timing on the No. 1 Plug Wire for sure ?
    Need to see it, hear it, that kind of thing to help on this one. Know what I mean ? It's a be there kind of thing to be able to actually hear it...
    Just stating facts, not trying to be weird or anything... Can you do a video on it ?

  7. #7
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    Check your valve adjustment, tight valves will lower vacuum and screw with timing, once valves are adjusted, set timing with vacuum advance disconnected.

  8. #8
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    How did you use the piston stop for setting the timing????

    Will it start with starting fluid sprayed thu open carb throttle plates????

  9. #9
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    That you needed a new mark on the balancer is a concern. How far off is the factory mark?

    Try popping the hood when you shut it off, let it cool down faster see if it helps.

    I had a couple of cars that did this, the problem was heat. The fuel in the carb bowls would boil, and the pressure would force the fuel out flooding the manifold. If the car sat long enough for the fuel to evaporate it would start fine. Otherwise I would need to crank it with the accelerator to the floor for five to ten seconds to clear out the fuel.
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  10. #10
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    One thing I forgot to mention is that once the engine is hot and I turn off the ignition the engine keeps running for for a few seconds (dieseling). That's why I thought the problem was timing. But as I said before I already tried adjusting the timing...
    The reason why I made a new mark on the balancer was because when I tried to check timing the mark on the balancer was way off so I thought maybe the outer balancer ring had slipped. But now I know it didn't as the new mark is also way off at idle, about 30* advanced.

  11. #11
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    350 bal on a 305 . been there done that. advance the timing as far as it will go before starting to blubber.

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    have you tried a "Smoke Test" there are a lot of youtubes videos to find a vacuum leak
    good luck

  13. #13
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    Quote Originally Posted by 47Fordcoupe View Post
    Hello everyone, I'm new here.. hoping someone could help me figure this out. So I recently purchased this car which has a 305 SBC in it. The engine starts right up when cold, but hard to start when hot. I already ruled out vapor lock as well as engine vacuum leaks. My vacuum gauge is fluctuating between 5" Hg an 7"Hg.
    Also my timing seems to be way advanced at 30* at idle and I can't bring it down without the engine stalling.. I did find tdc and checked harmonic balancer mark. Thanks in advance for your inputs.
    First thing I would do is to change spark plugs and install a QUALITY set of spark plug wires, along with new distributor cap and rotor. Inspect the interior of the distributor to insure that the weights are free to swing out and advance timing and that the vacuum line from the vacuum can to the distributor is free of cracks or holes. The vacuum, with a stock to mild hot rod cam, should be at least 15" Hg and the needle should be steady. Here's a tutorial for you to follow.......
    https://www.youtube.com/watch?v=SdlNwm8OHco

    Once you are through with the vacuum tests, do a compression test of the motor.
    Run the motor to bring the water temperature up to max
    Remove air filter assembly
    Use wire or string to tie the throttle wide open so the motor can breathe
    Number all spark plug wires and remove all spark plugs so the starter won't have to labor to turn the motor over
    Disable the coil so that you don't have any sparks to start a fire
    Key the starter and let the motor go through at least 5 compression cycles for each cylinder, as pressure builds on the gauge
    https://www.youtube.com/watch?v=X_tbksFYhl4&t=168s
    .
    Last edited by techinspector1; 07-27-2018 at 12:04 PM.
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  14. #14
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    Sorry, duplicate post.
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  15. #15
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    I did not see anyone mention that you have to disconnect a wire on the firewall . Then set timing to "0" after that reconnect wire that will set timing I believe the wire is brown with white strip it has a plug in it so you can disconnect it.
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