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Thread: New 496 wont run??
          
   
   

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  1. #16
    Dave Severson is offline CHR Member/Contributor Visit my Photo Gallery
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    Curious to hear what you fuel pressure is at idle when you get your fitting and gauge installed. Where do you have the vacuum hose to the distributor hooked up, ported or full vacuum? I ran a similar carb on an E-85 engine and ended up using a vacuum referenced fuel pressure regulator to keep the engine clean at idle, hard to say until you get an accurate pressure reading. Is this the same carb that was on it when dynoed? My two cents worth would be to get a fuel pressure gauge on it and see where the pressure is, check your needles and seats to make sure some little pieces of gunk aren't holding them open, then perhaps a fresh set of plugs. Cleaning them is good, but doesn't necessarily guarantee the plug is firing clean, once they've been fuel soaked they don't always get cured with just cleaning. Also, what are the plugs and what do you have them gapped at? You might also want to consider an initial timing at 10 or 12 degrees and back the total off to about 34 to get the initial run in on the engine. Just my 2 cents...
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  2. #17
    Camaro350 is offline CHR Member Visit my Photo Gallery
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    Thanks and yes I have watched that and other videos but most are on the same line as that one where it tells you what the adjustments are but not what they do and the effects on the carb and engine running performance when you do change them. I haven’t really found a video that really covers this well so I can really understand what I am changing inside that carb when I do those adjustments.

  3. #18
    Camaro350 is offline CHR Member Visit my Photo Gallery
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    Quote Originally Posted by Dave Severson View Post
    Curious to hear what you fuel pressure is at idle when you get your fitting and gauge installed. Where do you have the vacuum hose to the distributor hooked up, ported or full vacuum? I ran a similar carb on an E-85 engine and ended up using a vacuum referenced fuel pressure regulator to keep the engine clean at idle, hard to say until you get an accurate pressure reading. Is this the same carb that was on it when dynoed? My two cents worth would be to get a fuel pressure gauge on it and see where the pressure is, check your needles and seats to make sure some little pieces of gunk aren't holding them open, then perhaps a fresh set of plugs. Cleaning them is good, but doesn't necessarily guarantee the plug is firing clean, once they've been fuel soaked they don't always get cured with just cleaning. Also, what are the plugs and what do you have them gapped at? You might also want to consider an initial timing at 10 or 12 degrees and back the total off to about 34 to get the initial run in on the engine. Just my 2 cents...
    I should have the fitting any day I am curious as well but truthfully the engine builders dyno’d the engine with everything on it already it was almost turn key, the carb, ignition, fuel pump, all came with it and had been run with it. Not that something can’t break in between then and now, I did find my distributor cap damaged which I replaced.

    As for the plugs I have to measure them I don’t know what the gap is, but I agree it’s probably a good idea to change them.
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  4. #19
    Camaro350 is offline CHR Member Visit my Photo Gallery
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    Quote Originally Posted by Mike P View Post
    I realize this is not exactly a Holley Carb, but it's based on one.

    Fuel level on a Holley is set so the fuel level is at the BOTTOM of the sight hole. Above that level the carbs flood.

    If it was me I think the first thing I would do is drop the fuel level (in hot climates with todays gas I have found running the level even a bit lower to compensate for fuel expansion also helps



    .
    Yes I would agree but I read the manufacture information on this carb setup and they state that seeing it has the sight glass you should set the float level as a base where you can see half in the sight glass.

  5. #20
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    ..........................
    Last edited by DennyW; 01-22-2020 at 03:18 PM.

  6. #21
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    With only 6hg vacuum, I would be suspicious of the power valve opening and flooding, another reason I suggested closing the the idle mixture screws.

  7. #22
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    Six main functions of the carb: #1 would be to deliver the improper fuel to air ratio under all conditions. Hence EFI.
    (Sarcasm alert)
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  8. #23
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    Also, a single backfire can destroy the power valve (I seem to recall this is especially true for Holley, and anti backfire kits are available)
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    .............................
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  10. #25
    Camaro350 is offline CHR Member Visit my Photo Gallery
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    How do I know if a power valve is bad, what can I see if anything or what are the symptoms?

  11. #26
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    Gently seat/shut the idle mixture screw (close, turn in, righty tightly). If the motor runs with the idle mixture screws shut it is getting fuel from somewhere else other than the idle circuit. This would lead to a possible power valve bad or mismatched to motor vacuum. It is also a sign of a possible vacuum leak.

    However, vacuum leaks usually run lean. With your motor running rich, I would suspect high fuel pressure, high float setting or a mismatched power valve.

    Fuel pressure needs to be confirmed first (or at least do what another suggested and disconnect the fuel and see if it runs on the float bolt's fuel only OK), otherwise you're chasing your tail.
    Second would be to check the power valve to see what rating is marked on it, and change it to a higher vacuum rating..
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  12. #27
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    Quote Originally Posted by 36 sedan View Post
    With only 6hg vacuum, I would be suspicious of the power valve opening and flooding, another reason I suggested closing the the idle mixture screws.
    Din Ding Ding..... we have a winner! Run the carb dry and pull the metering plate(s) to see what number is on the power valve. It sounds like fuel is dripping past with that low vacuum signal. Perhaps the paperwork can give you the value too??? Or ask the OEM what they put in'em from the factory.
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  13. #28
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    Quote Originally Posted by Camaro350 View Post
    How do I know if a power valve is bad, what can I see if anything or what are the symptoms?

    It'll run but power sucks.
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  14. #29
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    The valve uses vacuum to open and close. When you stomp down on the gas pedal the vacuum in the manifold drops to a very low number, this makes the power valve open. So when you start with a low vacuum number of 6 inches.. the valve may already be opening and now you've got to much gas in the manifold - once you turn up the idle screw a little, the idle jumps way up because you've already got plenty of fuel in the manifold that you don't/didn't plan on being there. I'm not certain or familiar with that carb, if it is a Holley copy you can get a power valve eliminator and run without it. Or, see if you can get a different power valve with a lower setting?? But I think your vacuum signal is to low already.

    Again, talk with the OEM, the folks that built that carb can help you tune it best. HTH.

  15. #30
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    34-40 has summed it up.
    One caveat though, if you eliminate the power valve (which I don't recommend for the street), you will need to drastically richen WOT (wide open throttle) as the power valve adds fuel for that circuit.

    And, continuing to run the motor rich can (will) do harm to the motor. May I suggest you find a local tuner familiar with carburetors (check with your local car clubs for a recommendation) and get some hands on help before it costs you dearly.

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