nuvaring
I don't have this plane or engine but there a couple things that could be going wrong
When the engine quites do you see fuel stay in the fuel line or does it stop before it quites, like it runs out of gas? If it runs out it is just fine because that is suggesting that all the fuel had moved to the front of the tank and the clunck has no fuel to suck. Usually in the air, during a dive, the fuel will stay in the back of the tank. It is usually natural for the engine to increase rpm when pointed up.
If the engine quites when pointed down and there is fuel still in the line you LS or HS might be two Rich
Hope this makes sence
Good Luck
Cameron