For any given state of tune (and a functioning pump) - there can be a variable acceleration / stumble depending on the acc. pump shot. I don't know what the shooters are worth these days but trial and error has worked pretty well over the years. Sadly - there aren't a great number of us left with a stack of old carbs to sort through and grab a different part number.....but that has often been my course of action. I once saw a (brave) Holley rep drill one and cure a problem at a clinic - but its not the choice of mortals.

On my current carb, I replaced the shooter screw with a "high flow" (alcohol) replacement (has a machined relief) and the result was favorable without a shooter size change. So, be aware that a minor change of the pump shot can change the behavior of the engine ....... the lean stumble can be made to go away.


 
 Steve Metzger       Tucson, Arizona

The volume of the pump shot is determined by the stroke, which is controlled by the pump cam.  The squirter determines the duration of that shot.  Everything else equal, a #28 will provide the same volume over a longer time and #31 will provide the same volume over a shorter time.  Because of the difference in duration, the #31 will provide more fuel at a given throttle position, but it will provide exactly the same amount of fuel as a #28 for a full pump stroke.

Don't expect much from Holley about recommendations.  I tried that when I first got my carb, filled out every bit of info they asked for in the contact form, which includes stuff the average person probably doesn't have a clue about regarding the build of their engine.  The response was something along the lines of it's impossible for us to know what your engine needs and you have to tune it.

Regarding the .015" "gap"for the accelerator pump I saw in an earlier post, and loosening the screw to reduce drag.  It is not a gap.  It is a clearance check.  You are simply ensuring that nothing in the accelerator pump will bind at wot and possibly damage the carburetor.  Adjust the screw so you have no gap at idle and then check that you have .015" clearance at wot.  Do not loosen the screw after this.



Lawrenceville, GA

JDC

I removed the discharge nozzle this evening . It is #31 tube type. The plan is to call Holley tomorrow to see if it is a good match for my 292. 

The clearance check of the accelerator pump at wide open throttle has nothing to do with the actual performance at wot.  It is only to ensure that you have clearance so nothing breaks when the throttle is wide open.


Lawrenceville, GA

Don't do too much comparing of jets from one carb to another, they are sized to the Venturi of the carb as manufactured. It is definatly possibly and probable that the same carb can be used from a 289 thru a 429 because of compression ratio. A higher comp ratio demands a richer jetting.
I know Holley recommendations are for an accelerator pump arm but I make sure it's squirts even with a slight movement of the throttle if a stumble bothers me. Setting to wide open throttle is OK but I'm never there and drivability is my first concern period. The plastic cam on the carb linkage can be adjusted to find the correct feel for your car. Also make sure all the bleeders are clear...good luck.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Getting a stable float setting will do wonders for a "wet" carb. Raising and lowering the float level (within reason) will tune the jets a bit (richer or leaner a shade) so long as fuel is not running out the sight holes.
Probably will have to change to a larger accelerator pump "shooter" - its the device that makes the mixture richer as you open the throttle.  

 
 Steve Metzger       Tucson, Arizona

my new holley came with 65 main jets,installed 60s the stumble off idea came,just went back to65s stumble got,as well the fuel hear has more ethenall in summer months,and i am running 87 obtain.should go to mid grade i guess

The adjustable vacuum advance should be setup to give about 8 degrees of available advance. Turning the Allen Key CC shortens the Advance. CW gives more. There's probably 26 Degrees Centrifugal built into the Distributor. 8 Degrees Initial + 8 Degrees Vacuum+ 26 Degrees Centrifugal totals 42 Degrees. That's about where You want to be. Changing the Advance Springs to Lighter Ones will allow full Advance by 2500 RPM. The Vacuum Advance is probably set at 16-18 the way it is now. You can check by using a Timing Light and applying vacuum to the Advance and see how much timing changes. Use the Allen Key to adjust it. Asking the Holley Guys for advise is a good Idea. That's what they are there for. I am having a similar problem with My Buddies 390 Holley that We swapped along with a Cardone Distributor. I will be following Your results and maybe something will apply to the One I am working on.