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A properly set up carburetor and engine should not need this. My original quadrajet has updated idle mix screws, secondary rods, and converted to electric choke. Other than that it is all stock. I have a mildly built 350 with bumped up compression and a mild cam and stock everything else. One pump on a normal 30-60 degree day and it fires right up after 2-3 cranks and sits on the high idle step. Starts @900rpm and builds to 1200-1300RPM once warm. Slight tap on the throttle and it drops to the set 750rpm out of gear. If it is sub-30 degrees out I'll use two pumps and get the same startup behaviour. Once it's warm, if I park and go into a store or get some lunch and come back out to it, I just hop right in and it is a single rotation and it fires right up to the hot idle speed. There is absolutely no extended cranking or holding the throttle open at all to get it to fire up when warm.
I'm just curious why you would think that is? The throttle is set to provide the proper amount of air and fuel flow for the vehicle to idle properly(750rpm in neutral in my case) without toughing the throttle pedal. The only thing I can think of that would require a touch of throttle would be to help clear a rich condition in the manifold from it sitting or maybe a small squirt of gas from the accelerator pump to help get it going?
Not saying you guys don't have that experience. Just saying you don't have to. Just because you have always set up your carbs to need to touch the throttle to start them, doesn't mean you NEED to set them up that way.
Just because it's new, doesn't mean it is right. It's just like the difference between taking a new off the lot modern EFI vehicle with the stock, canned, good enough for everybody with every engine tune and then comparing it to the drivability, power, and economy of a vehicle that has even a moderate amount of tuning done to it. It's not uncommon on a stock tune to see 5-15% LTFT's on it as the computer adjusts everything to the specific conditions of THAT specific engine compared to the tune that is designed to work on EVERY engine of that model. The factory leaves a lot on the table because they are mass producing something to work for every specimen of that vehicle. If you took that new, less than 10k mile vehicle and gave the carb and timing a good tuning adjustment for the specific engine and environmental conditions, I bet you wouldn't have that problem any more.
Have you checked vacuum at idle,and have you checked vacuum advance cannister. Believe it or not low vacuum and/or ruptured vacuum advance cannister will cause a rich mixture. Not saying it's causing yours or not,but I'd definitely check. The reason is at idle you are supposed to have high vacuum and pulling fuel from the idle circuit only. When you step on the pedal vacuum drops and the carbureator adds fuel,it's signal to add fuel is low vacuum. So if you have low vacuum your carbureator is continually adding fuel because it things you are on the throttle,if you are on the throttle at cruise its still reading a low vacuum so still adding fuel for power. The vacuum advance cannister rupture which not only alters your vacuum reading,but also doesn't have enough timing to completely burn the incoming air fuel charge. That is the reason for the timing advancing is to light the fire early enough to burn completely. Also Edelbrocks don't like too much fuel pressure so might want to check that also. After you've checked those things if you haven't found anything ,we can dive deeper. Also if mixture is incorrectly or timing is incorrectly set,and you crank the throttle stop screw in to hold the throttle plates open so it will Idle, it draws fuel from the transition circuit and the idle circuit at idle.
