Re: Trouble running
As you know, Holly's are infinitely tunable, but horrible if not set up right. I have tuned a few Holly's and am currently running a 670 Holly Avenger 4150 in a '73 Nova with a 350 HO engine, 700R4 automatic, and 3:73 gears. The car is a 3800 pound, stock appearing, air conditioned, street driven sleeper and the carburation is right on.
It sounds like you have the pilot screws set about right, but also make sure the float levels and metering block jets are in the ball park (you can fine tune later). Once those circuits are close to right, you can move on to your most likely problem.
Now to the problem. If you have an off idle stumble, make sure your accelerator pump is squirting fuel and make sure to start with the middle length pump arm (again, you can fine tune later). Replace the diaphragm if a steady fuel stream is not observed.
You didn't say which model you have, but if it's a vacuum secondary carb, check the secondary throttle plate spring. Your problem is often caused by the secondary throttle plates opening too soon. Try replacing the secondary spring with the next step heavier spring. Buy the secondary spring tuning kit at a speed shop because you will need to try different springs to get it right. (They are color coded)
Assuming that your cam and ignition timing are correct, and your carb is clean with no leaks, a 650 will perform well on your engine, but depending on your tune, rear gears, and torque converter stall speed, you are close to over carbureting a mild 351 with a 650.