Silver00V6Camaro

Well im still fighting an off idle stumble. I have lars's paper on tuning a holley. can someone tell me how to adjust the transfer slots.
Carb: 0-80508-3
Brand: Holley
Product Line: Holley Model 4160 Adjustable Float Carburetors
Part Type: Carburetors
Number of Barrels: 4
Carburetor Flange: Square bore
Choke: Electric
Fuel: Gasoline
Secondary Type: Vacuum
New or Remanufactured: New
Fuel Inlet: Dual
CFM: 750
Carburetor Finish: Silver
Ford Kickdown: Yes
Throttle Linkage Type: Universal
Quantity: Sold individually.

Carburetor, Model 4160, 750 cfm, Square Bore, 4-Barrel, Vacuum, Dual Inlet, Silver

burners

The idle adjustment screw controls how much slot is exposed on the primary side. There is a little screw for the secondaries that you have to remove the carb to get to. It is nearly in line with the secondary throttle shaft on the side with the vacuum actuator.

Barry's70LT1

Can you provide some additional information on "off idle stumble".

A/ - Does it happen when you rev the engine quickly ?

B/ - Or, does it happen when you gradually increase the throttle, and when just off idle, you get a constant stumble until you increase the throttle position.

If (B), then this is likely the condition. The primary throttle plates (at idle) are almost completely closed. This in itself is not a problem. You can adjust the mixture screws and all is well.

However, when you slowly increase the throttle, the transfer slots are supposed to be exposed at about the time you leave the idle circuit.

If this doesn't happen, then at a certain position, the idle circuit cannot provide enough fuel, and the transfer slot has not yet been exposed.
The result is a flat spot just off idle, until the throttle is depressed/opened further to expose the transfer slots.

I have fixed this problem by slightly extending the transfer slot downward, so it becomes exposed earlier.

As this involves a modification that cannot be easily reversed, be sure that you have eliminated any other cause.

If you are sure this is the reason/cause for the stumble, then this will solve the problem.

If someone else has a better fix for this, I would be very interested, as I was unable to, without modifying the transfer slots.

Barry

Silver00V6Camaro

I am going by what was recommended by the holley tech I spoke with. I have delt with this problem for a year. I have a bigger shooter #35 and a 50 cc pump and yellow cam. Screws are turned one turn out. Its almost gone today when i drove the car so all thats left for adjustment is the blades. I have tried everything else.

dmaaero

I"ll try and tell you how to adjust the idle transfer slot. It requires removing the carb, turn it upside down ( if your not sure where they are let me know and i can get you a picture) take a .020 feeler guage and adjust the primary idle screw till the slot looks like .020
Now hold the carb up to a light and look up through the bottom at the crack around the primary butterfly, adjust the rear butterfly so it has the same amount of crack. From then on, if you adjust the front idle screw , adjust the rear idle screw the exact same amount.

lars

That's exactly right for a Holley setup. Did you attend one of the Tuning Seminars...?

Silver00V6Camaro

No i have not attended a tuning seminar. I just got your papaer on tuning a holley and what the holley tech told me and im going by those to tune this carb. Thanks for the help.

stingr69

Shouldn't you be using the black cam with the 50cc REO pump? I would be surprised if you actualy needed that either way.

If the slot is exposed to look like a square in shape when you turn the carb over, you are about there.

We assume you have zero slack in the accelerator pump linkage AND at the same time .015" additional pump travel available at WOT? If you have ANY slack at all it WILL stumble. This is the biggest possible cause. Lots of confusion out there about how to adjust the pump linkage.

One last thing - do you run manifold vacuum to the distributor advance cannister? The timing can back off quite a bit when you crack the throttle and cause the engine RPM to slow considerably. Not that it happens often but it has happened to me once. I tuned it out by running less ignition advance at idle. This allowed me to crack the throttle more and get the transition slot in the right place.

-Mark.

dmaaero

This guy right here taught me how to do it.

Silver00V6Camaro

The acc pump conversion comes with a yellow and brown. which both pump cams that came with the conversion are bigger than the black one. Yes everything is adjusted right actually I think im almost there anyway and i need to recheck the float. I got the car back from the alignment shop today and there was no backfire at off idle just a very slight (hardley and off idle stumble).

Fevre

69vettester

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