I just got my new motor running and im looking for some jetting help. The specs are: 383 w/ flat top piston, 62cc fastburn heads, 227/233 duration .496/.510 lift cam, rpm air gap, lt headers and 3" magnaflow catback.

I put a holley 750 dp on top and its running real rich. I messed with the air/fuel mixture screws and the plugs are burning white instead of black now.. It has a bog if i hammer the gas from idle, im assuming thats the pump shot??? How do i know what jets it needs? After i drive it for awhile the inline fuel pressure guage drops all the way down to 0 and it seems all the power isnt there, its hard to tell but it doesnt cut out, would this be vapor lock? Basically this is my first carb experience and i know nothing about them so any help would be appreciated. thanks

 

The carb circuits:
Idle - pulled into the air stream from under the throttle blades. The mixture is a combination of fuel pulled from the carb fuel bowl and air from orificed "bleeds" up in the air horn, as well as the air being pulled past the slightly open throttle blades. The idle mixture screws give a little control authority over the idle air/fuel mixture. It probably has very little to do with your black plug problem.
Main circuit - Fuel is pulled through the "booster venturi" in the main venturi when the throttle blades are open beyond idle. The fuel is metered by the jets, one for each "barrel" or venturi. There is also a little air bled into the fuel as it goes up to the booster venturi to help it mix with the air stream a little easier.
Power circuit - Under engine load, a richer fuel mixture is required than under cruise. Holleys use a "power valve", which is closed under high vacuum conditions, and opens when vacuum drops to allow additional fuel into the mixture. It goes through the booster venturi, but not the jets. Metering is built into the metering block.
Accelerator circuit - When the throttle is first opened, there isn't any fuel flowing through the main circuit. The accelerator pump squirts some fuel into the venturi air stream to provide the needed fuel until the booster venturi can pull fuel into the air stream.
Secondary circuits - all of the above are duplicated in the secondaries, with some possible differences, depending upon your specific carb model. Most don't have a power circuit, for instance, and many don't have adjustable idle mixture.

Your problem is probably related to the main metering and/or main power circuit. In other words, you need to rejet, and/or verify your power valve is closing (basically a physical inspection or replacement, possibly a power valve change to a different vacuum rating).

All of this information is available on Holley's website under their tech information links.

 

Thanks for the info five7! How can you tell if it running rich/lean at idle and then at WOT? Pull a plug ,clean it, and test that way?

 

Idle adjustment is pretty much a matter of maximizing vacuum. Main jets is reading plugs and performance.

Of course, all of this working right is dependant upon the ignition doing what it is supposed to do. Retarded timing will cause a rich mixture by itself.