Justa followup for the id on this carb...
The list 6426 is a Holley aftermarket performance 2300/centerhung bowl mixer. A somewhat rare 600cfm version (current version is 500cfm). Used primarily in "class" racing competition under various sanctioning bodies in circle track and some drag race classes.
The current list 4412 is more widely known/used, while the list 7448 (350cfm rating) is by far the most popular/suitable mixer for conversions on 304/345 motors.
Robert's version of initial float setting is right on. When building these carbs for IH apps, I invert the bowl and set the float where it''s surface (flat area) is absolutely parallel to the bottom surface of the bowl itself (eyeball method). That will be near perfect for a brass float, with a new Holley float needle assembly (viton-tip, not the steel or titanium alcohol needle). The intake manifold onna IH applicatipon sits the carb absolutely level when the rig is parked onna level surface, that is the starting point.
If equipped with either type of two different "plastic" floats, that level will have to be a tad lower, as those floats "float higher".
Once the engine is fully warm, then the actual fuel level setting is completed by removing the sight plug and tweeking the needle seat up or down as needed to bring the fuel level to just below (I run 'em 1/16" below) the bowl thread for the sight hole.
The standard fuel inlet pressure for all the oem-design Holley modular carbs is 5.5psi. The oem standard for IH production and any aftermarket replacement mechanical fuel pump is also 5.5psi nominal with a volume of 27 gallons per hour at 4000 engine rpm. That info can be verified in the "ct-404-l data book" document I posted last week. It's also contained in many Holley service references, nothing special about that spec.
The fuel overflow is coming from the bowl vent which is what it's supposed to do when the fuel volume control system malfunctions for whatever reason. Any carb fuel bowl system must be vented to the atmosphere in some manner.
On these modular carbs, never "bend" or tweek any portion of the float itself, if ya do that, you will never be able to "adjust" the fuel level correctly. I see tweeked floats all the time where someone has tried to adjust 'em like some other brand carb, just will not work! Some of these carbs are equipped with a non-adjustable float needle set and those must be used with a float that has not been butched. I prefer to not use those type needle/seats, I've got tons of new ones sittin' inna container.
