if you don't have one already, get an inline clear plastic fuel filter and install it before the carb. This will help trap rust and crud from the tank and prevent the needle jet from getting blocked.

Happy to report back that the problem is solved. Culprit; as everyone previously mentioned:  sticky needle and seat.  I made a temporary fuel bladder from an empty quart oil bottle and an old petcock.  At first, everything seemed to work as it should. With the bowl removed, raising the float stopped the fuel flow, but I did it a few times and got lucky.  I was about to put it back in for the third time, when I noticed no fuel flow, and jiggling the carb did nothing.  Removed the needle and seat, cleaned them, and re-installed.  Bingo.  The car started right off.  Thank you to everyone who chimed-in. Greatly appreciated!  Aloha.

When one works on a car and has unexpected problems, the first place to check is where the work was done. In your case, the change was installing a new carb, so you should have suspected the carb first. In my case, I had a flooding problem due to the sticking valve needle. My new car was straight from Burlen the manufacturer, so I didn't suspect it either. I suspected vapour lock and over-pressure, because the float is supposed to close the valve, right? I tried insulating the fuel line behind the carb, a pressure regulator, replacing the (working) mechanical fuel pump with a Facet electric (whose constant racket drove me crazy... OK maybe crazier), and then a proper electric SU fuel pump. Eventually I arrived at the carb. (Isn't hind-sight wonderful!). First pic shows the parts to install the fuel regulator and filter. 2nd picture shows them installed. 3rd picture show the final result without the regulator. The hard tubing is actually 1/4" brake line.

When this first happened, I was in disbelief.  I had a brand new carb on a running motor.  Fuel supply was my first thought. I drained my fuel tank and replaced the little Faucet pump. along with both fuel filters.  I have a filter on the supply line from the tank to the pump, and another just before the carb. Key on, fuel freely flows to the carb.  I'm not familiar with SU's.  I can't drain the float bowl.  I guess my next step is to remove the carb, again.  Remove the float bowl, and connect a fuel line to verify flow. Arrgggh!

Yes, I verified fuel to the carb.  Also, when this first happened, I removed the carb and quickly cleaned the insides with contact cleaner.  

+1 to Spank's advice.

Years ago, I bought a brand new HIF44 that did the same thing (and worse). After a range of other "fixes", including a fuel pressure regulator, I discovered my inlet needle was sticking. It was not gummed up, but would stick open, resulting in flooding, even while running. The solution was to carefully file off the 8 sharp edges of the needle so it had a bit more freeplay in body of the jet. The body of the needle is cross-shaped, so each of the 4 fins has two edges. If you go as far as removing the needle, round off the edges while you are at it, just in case. Not much - just a few thou of an inch off each one.

When you say "all good" on the fuel at the carb, are you saying there is fuel at the hose leading into the carb or that you are 100% confident that there is fuel inside the float bowl? Kinda hard to tell with the HIF carbs. Very often the little float needle can get stuck in the UP position which means it is closed. It gets gummed up by the gas that was once in the carb but then slowly evaporates leaving a sticky residue. The sure Fix for that requires you to remove the carb, remove the 4 screws of the fuel bowl plate and take out the float and pull the needle valve out and spray some carb cleaner in there and work it up and down. SOMETIMES you can get away with just wacking the base of the carb with the plastic handle side of a screwdriver and see if that works it loose enough for the 2-4psi fuel pump to push it down and flush out the gumminess from the float valve.

Thanks for the reply. Yes, the front in blocked off and the rear is attached to a tube running down in front of the fire wall.

Presuming you have an HIF44 carb, there're 2 ports on the left side (looking into the engine bay), the rear one is  the float bowl overflow and the front one is a vacuum port. Do you have the vacuum port plugged off or connected to the breather system like say the valve cover breather pipe?  

Need some help diagnosing my 1979.  I've got a 1275 in my 79' Mini.  Instlled a brand new SAU 44 carb about 6 months ago. Fired it up and ran it long enough to set-up the carb. Mixture, etc.  I drove the car about 20 miles , then parked it in the garage.  Had to leave it alone for about 5 months.  Yesterday, i started it up, and drove out of the garage.  I died as if I ran out of gas. Tried re-start. Nothing. Checked for spark. All good.  Check for fuel at carb. All good.  If I give it a shot of starting fluid, it fires right up momentarily. I've pulled the carb and tried a simple cleaning, but the carb was brand new.  I'
m stuck.  Can anyone offer a direction?  Thank you ion advance!!