What Jets to Use as a Base.

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Jan 9, 2008 | 06:10 PM

Bud2

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Bud2

Joined: Jul 2005

Posts: 1,237

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From: Warrnambool Victoria

What Jets to Use as a Base.

'72, L48 with a Holly 4160 (600CFM). I know it is running real rich, but what are you guys using as a base jet to start with?

Thanks.

Bud.

Jan 9, 2008 | 07:07 PM

Rdavis

Racer

Joined: Jun 2005

Posts: 400

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From: Lubbock Texas

Best place to start is the way it was jetted from Holley & tune from there.
You can look up the carb # here http://holley.com/data/TechService/T...%20Listing.pdf

It specifies the stock jetting power valves etc.

Jan 9, 2008 | 09:56 PM

birdsmith

Melting Slicks

Joined: Feb 2006

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From: Japan

Just as a point of reference I ran a Holley 600 cfm 4160 on a mildly cammed 350 with #60 primary jets; there were no overrich indications and it wasn't too lean either. Before you go the re-jetting route make sure you do all the proper calibrations beforehand- make sure the float levels are correct, check the accelerator pump lever to make sure the pump's not open at idle, set the idle air bleeds. If all that's good and it's still showing a rich mixture on the plugs then you'll want to start leaning the main jets down.

Jan 10, 2008 | 09:44 AM

lars

Tech Contributor

Joined: Aug 1999

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From: At my Bar drinking and wrenching in Lafayette Colorado

Quote:

Originally Posted by Bud2

'72, L48 with a Holly 4160 (600CFM). I know it is running real rich, but what are you guys using as a base jet to start with?

Thanks.

Bud.

You start with the stock baseline jetting and make sure everything is set up right. "90% of all carb problems are ignition problems." It is very seldom that a carb set up to its correct stock specs will be overly rich. Start with verifying that you have your total timing correctly set to 36 degrees and make sure your vacuum advance control unit is functional and hooked up to manifold vacuum. Then, verify your float levels and make darned sure you balance out your primary and secondary idle speeds so that the primary side does not expose any more than .020" of the transition slot. If you have more than .020" exposed and if the secondary idle speed has not been correctly set, your mixtures will be all screwed up. Once you have all this set up correctly, I will bet that you will not be off by any more than 2 jet sizes at the most.

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