52 Mercury engine

[oldford2]

I am stumped. Fresh engine up on the test stand. It starts first turn and idles smooth and quiet. Then as I slowly give it throttle it runs great up to a fast idle. Will run at a fast idle smooth forever. Then as I give it more throttle the accelerator jets squirt properly and the engine dies immediately even though the jets have provided the extra fuel. So I don't think it is fuel starved? I don't understand how it could die so quickly. If I let off on the throttle before it dies, it returns to a nice smooth idle. It has a Holley 9510 teapot carb which I know nothing about. I have the manual and compared to the simple 94 it is a complicated carb. Timing is right on. I only took the top off and everything is clean. Put a fine wire down what tubes I could access up top. Carb had sat on a shelf for 20 years so I could understand if it ran poorly. But the fact that it starts and idles great has me stumped. Any suggestions from folks that are familiar with the teapot?
Thanks