Holley 4160 Fuel Adjustment

Discussion in 'Engine Topic' started by gary 80z, Sep 9, 2009.

  1. gary 80z

    gary 80z Veteran Member

    219
    0
    Apr 2, 2009
    West ofChicago
    Tried turning the two fuel mixtures screws all the way in and nothing happens. The car runs a little rough but does not die. I have the idle set to about 800rpm. What would cause this? I'm adjusting it because I have black smoke coming out the exhaust and this thing will burn your eyes and throat if its in the garage at idle. I'm guessing too rich. Already checked the timing and that seems ok.
     
  2. nova75mike

    nova75mike Veteran Member

    281
    0
    Mar 20, 2008
    Etters, PA
    Check your float level, sounds like it may be WAY 2 high.
     
  3. ezcruisn71

    ezcruisn71 Veteran Member

    239
    0
    Jun 2, 2006
    SE, Michigan
    Make sure the power valve is not coming on at idle. If the vacuum is to low at idle the power valve might be coming on. If it is you will have to change the power valve to one that comes on at a lower vacuum than what your gauge is reading at idle. Also if you engine has ever backfired it could have ruptured the power valve causing it to dump fuel all the time.
    The 4160 idle mixture screw when it is turned all the way in is at max rich for idle. These carbs are the opposite from other carbs with the idle mixture screws.
     
  4. Damon

    Damon Veteran Member

    12,847
    2
    Nov 16, 2000
    Philly area
    Rick- only some of the 4160-style carbs have idle mixture screws that work that way. If he's got a typical 3310 or 1850 list number carb they are the more traditional in-is-leaner mixture screw adjustment.

    Agreed with above suggestions. Also, pop the carb off and check to see how much of the idle transition slot is uncovered at your idle setting. If you're uncovering too much of it (throttle too far open) you can be running almost entirely on the off-idle transition circuits at curb idle. Most common on larger displacement motors and/or with big lumpy cams.
     
  5. markw

    markw Veteran Member

    816
    0
    Jun 6, 2009
    Illinois
    Probably the transfer slots. You may need to open the secondary idle screw and close the primary idle screw to get the transfer slots closed down some. They should look like squares instead of rectangles when viewed from underneath. A blown (ruptured) power valve will barely run at idle, if at all. A power valve open at idle will not affect anything. The power valve richens the main circuit, which isn't flowing at idle or part throttle.
     
  6. Damon

    Damon Veteran Member

    12,847
    2
    Nov 16, 2000
    Philly area
    Agreed with Mark about the power valve, and for exactly the reason he states. Ruptured = bad, almost non-running at idle since liquid fuel will be sucked straight into the intake manifold under all running conditions. 'Open' at idle (vacuum rating too high relative to the vacuum the engine produces at idle) = no difference in curb idle quality.
     
  7. ezcruisn71

    ezcruisn71 Veteran Member

    239
    0
    Jun 2, 2006
    SE, Michigan
  8. markw

    markw Veteran Member

    816
    0
    Jun 6, 2009
    Illinois
    I wish Holley would call '1/2 the idle vacuum a 'ballpark number that should be fine tuned later'. To call it a 'rule' is totally wrong. Along with 'Carb size = cubic inches X 2 ' and 'Acc pump shooter size = (carb CFM / 2)/10'. The '1/2 idle vacuum' or the '2 inches less than idle vacuum' might put you in the ballpark or it might not. Idle at 1000 rpm with 14" of vacuum. Idle at 900 rpm and 11" vacuum. Slow the idle to 800 rpm and vacuum drops to 8". Drop to 700 rpm and you have 5" of vacuum. What power valve should I use? Here's how I do it. Start with a 3.5 valve. (Something obviously too low.) Go out and find a long hill and run in 2nd gear watching the vacuum gage. Push the gas to 10" vac and feel for surging or bucking or any signs of running lean. Air/fuel meter will help but isn't required. If it's ok try it at 8", then 6" and so on till you get lean. Note the vacuum reading and install a valve 1-2" higher. Now when you accelerate under load the valve will open just before the motor gets too lean. If it opens any sooner the motor gets 6-8 jet sizes richer without needing it. Idle vacuum is irrelevant to the power valve. I think Holley is just trying to get you in the safe ballpark but I wish they would explain it better. Some people see it as a rule and it's not.
     

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