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Thread: Holley Model 2010 with Solid Nozzle Bar Screw

  1. #1

    Default Holley Model 2010 with Solid Nozzle Bar Screw

    Hello, I'm Brian and a brand-new member from Central New York.

    I have a Holley 2010 carb (marine) that I'm rebuilding.

    In rebuilds of other carbs, the nozzle bar screw has been hollow
    to allow the accelerator pump to discharge through it.

    The nozzle bar screw on this carb is solid and I'm stumped as to
    how the accelerator pump can work like this?

    There is no way the accelerator pump can discharge with a solid
    screw blocking the discharge hole.

    If I place the nozzle bar on the carb, without the screw, and press
    down on the hole where the screw goes with my thumb, I can get a
    nice squirt from the accelerator pump.

    With the screw in place, I get nothing.

    I wonder how it ever worked?

    I notice that Holley has hollow nozzle pump screws.

    The one I have is 1/4-28 and 1" long. Can I buy a hollow replacement?

    Thanks for your time. Brian

  2. #2


    Hey Brian, the screw that hold the accelerator discharge nozzle can be solid or hollow on Holleys. The solid screws allows gas to come around the body of the screw and out the discharge nozzle, but are only good to displace x amount of fuel. The hollow screws are a must if you upgrade the accelerator pump to the 50cc units. Yes, you can buy the hollow screw if you feel you need it. Unless you're running the a huge accelerator nozzle (size 37 or bigger), or the changed out to the 50cc accelerator pump, it's not necessary.

    121-7 hollow Phillips head
    121-8 hollow socket head

  3. #3


    Hi 69cam.
    Thanks for replying. I've been checking several
    times a day to see if anyone replied.

    I understand what you're saying and thought
    that myself. But...with the screw in place,
    the accelerator pump diaphragm won't even
    squeeze at all and with a lot of force, I might
    get a drop out of the nozzle if I press for several
    seconds. Definitely not a squirt and not the quick
    shot needed to prevent stumble on acceleration.

    Is there any negative to have the hollow screw?

    If the squirt is too large with a hollow screw, will
    that hurt anything?

    Does it matter that it's a boat and not a car?

    Thanks for your time, I really appreciate it. If
    we can get out on the water soon, my wife will
    appreciate it too !


  4. #4


    Brian, I don't mind helping at all.
    First thought is to make sure that is the right screw.
    I found a break down diagram of your carb and that screw looks different then a Holley DP car carb:
    Have you messed with carb? Do you know if that is the original screw?
    You certainly can put the hollow screw in there. It's not going to hurt or negatively affect anything. (Worst case is it still not allow the FULL AMOUNT THROUGH if wrong hollow screw.) The hollow screw will not determine how much fuel gets delivered (unless screw is restricting flow). That is determined by accelerator pump and size of the accelerator nozzle. Actually the pump cam and nozzle are used to determine how much & how long it takes for it to deliver the pump shot. So you won't have to worry about that.
    As you stated the pump shot is just needed to get over the initial hesitation that occurs from air being able to react quicker then fluid (gas).
    So you just need to adjust the linkage so the pump shot reacts instantly when accelerator linkage is depressed, and it's a good enough shot to over come hesitation.
    If this carb has been unmolested and worked on the boat, I wouldn't think you would need to make any changes unless your just trying to fine tune things.
    If you don't have a performance shop around you can try your local auto parts house, O'Reilly by me actually has those on the shelf. Don't know if it will be the right thread for your carb, but they actually had the hollow screw.
    Last edited by 69cam; 07-14-2014 at 01:44 PM.

  5. #5


    Hi 69cam

    The carb, as far as I know, is from 1993. Anyone
    could have messed with it and it could be the wrong
    screw. Not sure why someone would change it, but
    I've seen a lot of things that have puzzled me. The
    only way gas gets by this screw is through the threads,
    which is virtually nothing.

    The link to the diagram (thanks) is the one I'm working
    from here too. It's unclear what type of screw it is from
    the diagram.

    Two years ago the carb worked fine with the exception
    of a stumble on acceleration (we now know why), but if I
    accelerated slowly, it worked ok.

    I ordered the screw you mentioned (121-7) today and should
    be here Thursday.

    I'll install it and post back the results.

    One other question . . . . . Under the screw we're talking about,
    there was a ball bearing and also a new ball bearing
    in the carb kit. Seems like this is a check valve of some sort,
    but it does not show up on the parts diagram?

    Instructions say to replace the ball bearing if you have one
    originally. But . . . . won't the ball bearing block the end of
    the hollow screw when it moves and it'll be just like having
    a solid screw?

    I think I should leave the ball bearing out. Any thoughts?

    Thanks again . . . Brian

  6. #6


    Hey Brian, I spent some time tonight looking around for a manual, break down with part numbers and for the life of me I'm not having any luck with that.
    First thing I would do is call Holley Tech support. They can clear up part numbers and possibly tell us if the nozzle screw is some 1 off or what not. I would be pretty sure that is has to do with the length of threads and how far the threads may go past where the fuel enters that nozzle chamber. I would call first thing in the morning to not have to sit and wait to long. Should clear some things up really quickly.

    I found some instruction on the rebuild of the 2010 and it says to compare the ball bearing from what was in there vs what was in the kit. If the same then replace. My thoughts is that as long as its not dripping fuel out the nozzle the original is fine. Not to mention if the new ball is to big and you put it in there it may be a booger to get out.

    You want that check ball in there. What will happen is that as the velocity of the air increases in the carburetor/venturis it will draw a vacuum on the pump nozzle if the check ball isn't in there and it will drip fuel into the carb as you are running around. It may or may not drip at idle but as the velocity of air increases the vacuum on the nozzle will increase causing it to drip fuel out of the nozzle when not needed. Also, if it does drip at idle it may load up as your idling through no wake zones and when you go to take off it may bog initially because of excess fuel dripping in. I might be over thinking it but something to consider.

  7. #7


    Yes correct. I installed a 50cc in carb, hollow screw and running 5.0 nozzle...still stumbles from a stop. This carb Street Avenger is junk - $400 paper weight.

  8. #8


    Well 69 customs, before just saying the carb is junk, you need to see exactly what is going on.
    Is the timing set properly?
    Is the timing advancing properly?
    Do you have a vacuum leak?
    A 5.0 nozzle doesn't sound right.
    I've seen them labeled in the 20s - 40s range.
    Do you have the accelerator pump linkage adjusted properly,
    to where it instantly starts injects gas as your apply throttle?
    Just because you changed to a 50cc pump doesn't change anything.
    You need to change the pump cam and pump nozzles to take advantage of the 50cc pump charge.
    Are your main jets to small?

    Could be several things that need to checked.

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