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  1. #1
    Join Date
    Feb 2016
    Location
    Surrey
    Age
    53
    Posts
    85

    Holley fuel starvation ?

    Hi

    rather strange issue with my new engine it’s a Chevy sbc with Holley 750 HP carb edelbrock performer heads etc etc Anyway when braking hardish at low speed when you put the clutch in at the same time the engine almost cuts out even stalled a couple of times. It’s very much I believe fuel in the carb as it responds almost immediately and I can make it happen easily. It’s a bit disconcerting as my engine builder hasn’t experienced this before but agrees it’s fuel in the carb thinks it could be the level of the carb ?
    Anyone else experienced anything like this?

  2. #2
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    794
    I installed Holley Vent Whistles, P/N 59-10 and it cured my problems. Mind you, I put them in the primaries and my carbs are mounted backwards. I'd suggest putting one in your secondary bowl to keep fuel from sloshing up the vent tube while braking.

    Here's a bit of info:

    http://www.cobraclub.com/forum/showthread.php?t=60685
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  3. #3
    Join Date
    Mar 2006
    Location
    Oxfordshire
    Age
    67
    Posts
    1,622
    Howard,

    Funnily enough on the way back from the Thames Valley meet my started stalling under hard braking too - must be contagious!

    John is spot on - it's the opposite of fuel starvation.

    In its natural production Chevy setting, the engine is tilted up at the front. This is why the intake manifold is angled, so that it brings the carb back level. However, with the engines in our cars being level on the mounts, the manifold tilts the carb towards the front. With the fuel bowl vents being on the inside (i.e. next to the venturi), under hard braking the fuel in the secondary bowl sloshes forwards, exits through the vent and thus gets dumped into the secondary venturi - creating a rich stumble. If the secondary float level is correct this usually only happens under very hard braking, but if the float level is set too high you will get this problem.

    If your carb is a 4150 or 4160 you'll have centre hung floats, and the float level is either in the centre if you have glass inspection windows, or to the bottom of the thread if you have the more common removable screw-in brass sight plugs.

    To lower the float height, slightly undo the large slotted lock screw, then turn the adjuster nut clockwise. This seems counterintuitive, as you'll actually see that this casues the fuel level to rise. This is because lowering the float height pushes it down into the fuel in the bowl, thus temporarily increasing the level. So you'll need to manually open the secondary butterflies by turning the slotted cam on the left hand side of the secondary shaft to burn some of the fuel - you should then see that the new level is lower.

    My level was spot on when I adjusted it last year, but when I checked it today after it stalled a couple of times on the MOT brake test I saw that the fuel level was level with the top of the sight glass rather than in the middle. I suspect this is because the secondaries spend most of their time closed, so the rubber tip on the needle valve gets compressed over time, this needing to travel further to shut off.

    If you're going to Tony Goff's meet at The Ely next month I'd be happy to take a look at it for you. BTW, I'm surprised your engine builder had never encountered this problem, as it's very common!
    Last edited by conrod; 24-07-19 at 12:00 PM.
    Alan

    CRC Thames Valley Regional Rep
    UK Rep for European Cobra Club (eurocobra.boards.net)
    Dax 427 DeDion - Huddart SBC 383

  4. #4
    Join Date
    Oct 2006
    Location
    Toton, Nottinghamshire
    Age
    46
    Posts
    846
    I had experienced similar on idle whilst waiting on a steep incline (either up or down). I found the float level was set too high on the secondaries.

    Russ.
    Joint Area Rep - East Midlands Region
    1984 DAX Cobra
    Rover 3.5 V8 with Holley carburetor.

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