I've been wrestling around with every video, article, forum, and bugging my friends about Holley noggin/lean backfire/hesitation for almost two months. I have had the carburetor off and apart numerous times. In the process I have learned about the subsystems and adjustments. Nothing I did had any positive effect, until I pulled the carb the first time. You can see in this photo that the previous owner, an experienced hot rodder, had put a lot of thought in the detailing as he mounted the carb.

We could not get the car to run right and the first thing I did, wrongly was yank the distributor and start messing with the timing. Then I began to replace secondary springs and idle cams, ultimately replacing the nozzle. One point there was a lean backfire that was very powerful and which I'm sure killed my power valve. Everyone wanted to start yanking at the jets up front, but I had noticed changing the springs and the idle cams seemed to help. I finally decided to replace the existing nozzle, going up from .31 to .35. When I pulled the carb this is what I found.

I went out and bought a stud kit for the manifold and bought a set of gaskets and a spacer and retorqued the carb back to the manifold. I now have to go back through the process of selecting the right cam and springs again. I replaced the power valve with a 6.5. The one in the carb did not have a number in it. The car responds well now. Here are a few things that show the difference.