This darn Diablo I could pull and pull and then all of a sudden, it would fire up and practically take off right out of my hands. Not the typical starting as noted above. Went through the carb several times. Went through the ignition several times. Same thing.
Then I got to looking at the choke plate

The choke plate the HR3A and HR14A should have is the plate on the left which has no holes in it. I occasionally see a carb with the plate in the middle with the single small hole and some others with the plate on the right which has a much larger hole. Guess which plate this Diablo had in it? Grrrrrrrrrrrrrr....

I took that plate off and installed a plate without holes and problem solved.
And when I think of this, it makes perfect sense. The Diablo Hirth Motor needs full choke (and I mean a full choke) to pull gas into the motor. With the large hole in the throttle plate, it was like my choke was not full closed. So when I pulled and pulled and pulled and finally got enough gas into the motor, it started and immediately was lean enough to take off.
I hope this helps someone else who may be struggling to start their Diablo.
Bruce