Fuel System help please

Maybe accelaerator pump cam; you can change them to suirt more or less gas initially to relieve bog. I'm no expert though so I suggest calling Holley or visiting their website for a better explanation and other causes.

Vacum leak, dirt in the needle valve, or to much fuel pressure.. the 2nd two are for the flooding.

Since you've tried two carbs with the same results, it's likely not the carb. What kind of fuel pump do you have? If it's an electric pump or a high performance mechanical pump you may have too much fuel pressure. Your engine needs 4-6 lbs of pressure at the most. You can install a regulator to set it where you need it. High fuel pressure will cause too high a float level since the needle and seat are forced open by the excess pressure. Since you messed with the idle screws, try resetting them by gently screwing them in until the seat, then backing them out one and a half turns. This is close enough to get the engine started and idling on its own. Also what is the basic condition of your engine? Worn engines don't produce enough vacuum to make carbs work correctly, you can get a good idea by checking the plugs. Wet plugs that smell of gas would be a carb or ignition problem. Plugs wet with oil or heavily carboned plugs mean the engine is the problem. Speaking of ignition, if you're still using the original points ignition, make sure it's in good shape. There is nothing wrong with points, but if they aren't 100% they can drive you nuts because weak ignition has all the symptoms of rich carberation. A 600cfm Holley is a great choice for your 302 and should be just fine out of the box, but I think you have other problems somewhere. Let me know what you find.

The accel pump on Holleys is nothing more than a rubber diaphram and a spring, so there's not much to go wrong. If it looks torn or the spring is rusty or broken, then you could swap them out easily enough. But I'm kind of confused, in your first post you say it's running rich, but then you say you richened up the idle mixture screws. To really know what's going on you need to pull the plugs and read them as best as you can. Most people think they have a fuel-rich mixture when instead it's too lean. If you step on the gas and the car pops, hesitates or dies, it is too lean. I've run several cars with 2x4 carbs in the past and although they were over-carbed for street motors, they started, idled and drove just fine. But the only way to tell is pop out all 8 plugs and see for sure.

I just re-read you first post as well. When you say that gas was "spewing" from the sight plug hole, do you mean it pouring out or just a trickle? A trickle is just fine and actually what you want. Try this: take the front bowl off the carb and hold it upside down. Gently pick the float up and gently let it settle down. When you do this the float should sit basically parallel with the bowl. If you adjusted it all the way down, it's too low and further leaning out your mixture, since the main jets need to be submersed in gas.

Any fuel comming out the acc pump squirters? If you cant move the arm, the feed passage to the squirters might be plugged. That would also cause a big hesitation, or small if a little fuel comes out. Part of the prob maybe that it's probably not a new carb, but a rebuilt one. I'd get a rebuild kit and change out all the gaskets etc on the chance that you have the wrong ones in there somewhere.

Ok, now I understand. I'm kinda dense sometimes (ok, most of the time!). Anyway, as you've already discovered, there isn't much to the accelerator pump on a Holley. I would pull the bowl off and then pull the accelerator pump cover off and see if the little pump arm moves freely. It should be very free, almost to the point of being loose. Then either blow air or squirt some Brake-Kleen in there to make sure the passage in the bowl for the accel pump is clear. Then inspect the diaphram VERY closely for rips, or some sort of manufacturing defect. New carbs are not always perfect. I bought a Holley from Summit one time and after a week or so the plastic float sank, flooding the whole top of the engine. I called Holley's tech line, explained the problem and a week later they sent me a new float, a set of gaskets and a letter apologizing. Anyway, once you get the pump cover, diaphram and spring back in place, give the lever a couple pumps by hand to make sure it moves freely and that it pushes air away from the hole in the bowl. There's only three parts to the whole thing, the cover the diaphram and the spring so one of them is causing your problem.