Unless your 800DP(4780) carb has been modified, that’s a 2 corner idle carb.

That’s not likely going to work very well with your combo.

If it’s been modded to have 4 corner idle, then you’ll need to measure all the orifices in the idle circuit to see what you have.

What you really need is a carb with “race calibrated” low speed circuits....... something like the original HP950.
For a new style carb, something like a Race Brawler or QFT Q series is the type of carb you should be looking at.

The reason the 50* helps is because it increases the carb signal when the blades are closed.
The reason that’s necessary is because the carbs you’re working with are designed to operate with fairly normal manifold vacuum...... which you don’t have.
The race calibrated carbs are designed to operate at much lower manifold vacuum.

I’d still recommend the leak down test.