Help with 340 compression + cam change

midnight340 said
fuel to the motor it means the carb is too big, not too small. It's the mixture we are going for, and a large carb will feed so much air that it's hard to get the right amount of fuel.

That's a BS explanation. On a larger carb it can be more difficult to get good response on the idle circuits and if all other things are equal, will be at a higher rpm before there is enough velocity through the boosters to get the main circuits going.
At wide open throttle, especially with mechanical secondaries, there's less manifold vacuum with a larger carb. This potentially can mean more power if fuel-air distribution to all cylinders is really good. There is a diminishing return because the vacuum is helping the fuel droplets stay well distributed and available to each cylinder.

midnight340 said
And also, someone here had posted a video talking about how a smaller carb helps with the velocity into the intake, giving more torque at the bottom end. And, besides street performance, the video talked about how a smaller carb will often win on the strip due to the influence off the line.

Sortof. More velocity at lower rpm gets the mains started earlier and the main circuits are generally more responsive and efficient than the "idle" circuit.

midnight340 said
All of this says a smaller carb is good, but then I always hear how the 340's LOVE bigger carbs!!! Makes it damn hard to decide whether the 650 or the 800 would be best.

Tough call! There's no absolute answer. If you shooting for a mph goal at the end of the 1/4, then the 800 has more potential (assuming the tires and gearing are such that the engine will be near its peak at the stripe). The 750 Eddys need some work to run to their potential. So on that series, the smaller carb is a better choice. For the AVS2, can't say, but I think for your situation you made a good choice. You can always go back to the 750.
I was running a 650 vacuum secondary Holley for a while. Just a little less cam than you have. It ran just as good as the 750 on the dyno. Don't recall taking any 1/4 mile passes with it, which would have been a better comparison.

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