Good to see that our doing a lot of homework. The most common 2-cycles, like the Yamaha KT-100 and the Rotax, have external pulse lines attached from the crankcase to the carb. The Leopard has a passage through the reed cage, eliminating the problems of dried out or pinched line.
Your theory on carb operation is a little off. The pulse pressure only affects the pump side of the carb, raising and lowering the pump diaphragm. This action pumps fuel into the carb chamber, similar the float bowl on a car. None of the pulse is felt at the tank. The amount of fuel in the chamber is regulated by the needle valve. You saw in the video, that he tested the pop-off of the needle valve with a pressure gauge. The more tension on the spring, the more fuel in the chamber and vice verse. also in the video, he set the pop-off to 10 psi, + or – 1, and that’s a good place to start. IMO, compressing the spring will get the proper pop-off for now but will eventually go back to it original tension. If you have the patience, you can cut little pieces of the spring off to lower the proper pop-off. I think the best way is to purchase a kit with several springs of different tension. If you don’t have a pop-off gauge, get one. Eventually you’ll need one. But to get your engine to started start, just about any pop-off will do so long as it not too high or low.
Also look at the gasket between the crankcase and the reed cage to make sure the pulse port hasn’t been blocked off. And hate to asked this, but does the engine have compression? It’s a 2-cycle engine. All you need is fuel and air plus spark at the right time and compression.
Keep plugging away on this.
LAD Specialties customer / tony kart / rotax / kt100