Holley 4150 Squirters & Pump Shot - part II

Discussion in 'Engine Topic' started by EricsZ28, Oct 6, 2009.

  1. EricsZ28

    EricsZ28 Veteran Member Lifetime Gold Member

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    I'm making solid headway in eliminating my off-idle stumble. The engine would stumble when rev'ed - even at idle. The carb is a Holley street HP 650 DP (ms).

    So far, I've stepped up to 35 squirters from 28's. I've set the pink pump cam on the first hole (it was on the 2nd). I've tweaked my accelerator pump linkage (took out a bit of slack - probably from messing with the cam). The stumble is now greatly reduced, but not completely gone.

    I have 3 questions before I make any more changes:

    First, is it normal to have to shim the accelerator pump linkage? Mine had a little slack, so I've tightened it up a bit (by loosening the nut) and the engine responded well. Beyond a certain point, the engine stopped responding. Now I'm concerned that I'll over extend the pump at WOT. Thus, I'm thinking I need to shim instead. Is that normal/correct?

    Second, do I need to change the discharge nozzle's screw when I go to 37 squirters, or is it for anything greater than 37's that I switch the screw?

    Third, when do I make the call to switch to a 50cc pump? Is it when I run out of gas on the pump shot with the larger nozzles? Or is it by default when you get to a certain nozzle size? I'm assuming it's when I run out of gas... I had (on my previous carb) 40 squirters and a 50 cc pump - and it would flood the car out on part throttle.

    Thanks!
    -Eric
     
  2. 1980RS

    1980RS Veteran Member

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    You should have no slack in the pump arm unless you are drag racing then you can add slack if you foot brake the car and want all of the squirt.


    The rule of thumb on the screw is anything over 40 you are suppost to change to the hollow screw. I have not seen any benifit from it but others do.


    As for the 50cc pumps I only use them on the street if I have a very tight converter otherwise I have always used as small of a squirter as possible to try to eliminate the bog and to not make it too rich also.

    One other note, I was at a dyno session one day and was watching as the guy did a pull. when the engine was at around 4K I watched as the nozzles pulled a lot of fuel over into the engine after the carb was already at WOT.
    I said something about this to the operator and he told me I did not know what I was taking about. I replied that this engine should have anti-pullover squirters. After seeing this It could screw up things a little. Just something I thought I would pass on to ya.
     
  3. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

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    What you are doing, by over tightening the accel pump adjustment (you should always have some slack left at WOT so you don't hurt the diaphragm or bottom it out completely) are compensating for a pump cam that does not ramp up fast enough. I am guessing you need a pump cam kit. I found the stock pump cam on the dp carbs to not enough intial hit even bumping the shooter size up as well.
     
  4. EricsZ28

    EricsZ28 Veteran Member Lifetime Gold Member

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    Is there anything that shows the "ramp" for each cam color?
     
  5. Mwilson

    Mwilson Veteran Member

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    another thing that will make a big difference in hesitations is power valve opening, most carbs come with 6.5 and I usually end up at 8.5 to get rid of hesitations.
     
  6. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

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    Copied from www.carbdford.com

    [​IMG]


    Volume delivered for 10 strokes of the pump with a 50 cc pump

    Pump cam position number 1
    White 17cc
    Blue 18cc
    Red 18.5 cc
    Orange 19cc
    Black 19cc
    Green 24cc
    Pink 30cc
    Brown 36cc

    Pump cam position number 2
    White 19.5cc
    Blue 20cc
    Red 20 cc
    Orange 24.5 cc
    Black 18 cc
    Green 30 cc
    Pink 37.5 cc


    Rating of pump cams by fuel delivery over the first 30 to 40 degrees of throttle spindle from from the idle position. Pink is the least pump shot and yellow is the biggest pump shot.
    1 - pink
    2 - black
    3 - red
    4 - white
    5 - green
    6 - orange
    7 - brown
    8 - light blue
    9- yellow
     
    Last edited: Oct 6, 2009
  7. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

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    So the pink cam delivers the smallest initial pump shot and spreads a large volume out over time.
     
  8. EricsZ28

    EricsZ28 Veteran Member Lifetime Gold Member

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    Thanks Steve!!! That explains things a little more clearly. I guess I'll pick up the cam kit and a few more squirters. Right click, copy, paste, save...

    Mike - I've thought about that as well. I pull 13.5" of vacuum at idle, so I figued a 6.5 was OK. But I've seen a few people suggest this. I'll pick up one of those as well.
     
  9. markw

    markw Veteran Member

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  10. Damon

    Damon Veteran Member

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    If you're already at a #35 squirter (7 over stock) and you still have a stumble something else is wrong with the carb or your ignition (never overlook ignition-related issues). Most holley-type carbs are marginal with a 25 against a tight converter, borderline low with a 28, fine with a 31 and overboard with a 33. Never had to go over a 35 ever.

    Stop going bigger on the squirter. Try a different pump cam (orange is an excellent choice when you don't know where to start). If that doesn't help you need to look elsewhere for your problem.

    Remember that the bigger the nozzle the shorter the duration of the pump shot (delivers the fuel faster so it takes less time to drain the accelerator pump). So there are limits to how much a bigger nozzle can help.
     

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