I don't think the new carb will help. Please remember that the engine ran great with Mx X carb and doesn't need the improved carb to run. Remember that these toy engines run great with fixed venturis. It sounds like you are having a fuel draw problem. This is he opposite of the way you discribed the problem earlier. The glow plug shouldn't be an issue if you are leaving the glow plug drive on. I have to ask since the needle may have been reversed could the carb's spray bar be installed upside down? The cutout (fuel discharge port) should be pointed towards the engine.

The new 2600 carb is an improvement with regards to midrange and transition. There is no improvement as far as how strong the engine runs or for ease of starting.