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Old 07-10-2004, 09:09 PM
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Holley 4150 choke horn

Hi, got a older Holley 4150, 600cfm DP, mech. secondaries,and was wondering if anybody ever milled the ckoke horn,and if it is worth it to try and smooth or increase air flow. Intake is a single plane edelbrock,and I know a mech. sec. carb with single plane intake isn't best choice for street, but the combo actually works pretty decent on my 327. Thanks.

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Old 07-10-2004, 09:19 PM
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I have on a lot of carbs.

I don't reccomend it unless you are having air cleaner clearance problems. Your carb will always run a little lean.

You are better off going with a larger carb if you want more airflow.
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Old 07-10-2004, 09:29 PM
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choke horn

Why would removing choke horn lean out carb?
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Old 07-10-2004, 09:33 PM
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It increases the airflow past what the air bleeds and the fuel restricion orfices were calculated for.

I have milled Holleys, used bigger baseplates, added secondary idle circuits, etc. I think you are better off buying the right carb.
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Old 07-10-2004, 09:59 PM
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carb

have any luck using stubstacks? Think using 4 hole base gasket would benefit, cause I figure with my setup, I need good fuel atominization when fuel hits plenum floor.
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Old 07-11-2004, 08:34 AM
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Simply milling the choke horn down flush doesn't increase the flow. In order to see any real gains you have to blend it completely down to the venturies so that it resembles an HP series carb. It would be much easier to by a proform main body. The proform main body also has screw-in air bleeds.
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Old 07-11-2004, 02:22 PM
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Re: carb

Quote:
Originally posted by vetteman
have any luck using stubstacks? Think using 4 hole base gasket would benefit, cause I figure with my setup, I need good fuel atominization when fuel hits plenum floor.
I have used those too. Same thing, it causes the carb to lean out. Simply increasing jetting doesn't fix the problem either. Jets are for cruise. The PVCRs (the holes behind the powervalve) control WOT operation.

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Originally posted by tresi
Simply milling the choke horn down flush doesn't increase the flow. In order to see any real gains you have to blend it completely down to the venturies so that it resembles an HP series carb. It would be much easier to by a proform main body. The proform main body also has screw-in air bleeds.
Milling the choke shroud alone does increase the CFMs. Not as much as blending the radiuses as you mentioned. Milling it down flush sees its biggest advantage on low clearance air cleaners. You need at least 1/4" clearance above the air horn for a Holley to work. Increasing the clearance from there further promotes airflow increases.
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Old 07-12-2004, 10:41 AM
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??

77,
Are you sure this is a true statement

( have used those too. Same thing, it causes the carb to lean out. Simply increasing jetting doesn't fix the problem either. Jets are for cruise. The PVCRs (the holes behind the powervalve) control WOT operation.)

At wot both the jets and the pvcr's control the amout of fuel going into the boosters. That is why drag racers change jets to lean or richen the motor under full power runs.


Keith
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Old 07-12-2004, 05:09 PM
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You are right. It is a combination of the jet area and the PVCR area that control WOT performance. But, on your everyday street driven Holley, people don't usually drill their PVCRs larger or press in lead shot to make them smaller. They usually just change the jet sizes.

Most credible carb gurus say that you should not increase your jet size by more than 4 sizes from the out of the box settings. This is because the you will end up running rich on your cruise in order to achieve proper air fuel mixture at the top end.

Jets actually start flowing at moderate cruise, and can even have some effect at idle. They are not the top end only metering orifices that everyone confuses them for. They also can't be used to make a carb that is too big work on an engine that is too small, and vice versa.

Drag racers increase or decrease air bleed sizes, PVCR areas, and jetting together respectively. Fine tuning may only require one of the orifices to be changed, but they all need to be modified together when a major change is made to the carb's metering.
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Old 07-15-2004, 12:36 PM
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Choke Horn Removal

If the choke horn is not taken off properly, and the carburetor is not recalibrated you can do more harm than good. You're generally going to be better off getting a carburetor that is closer matched to the application.
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