So there is a float in youre carb. When it is floating, the gas stops coming in. if it is not floating, the gas keep coming, and floods up into the carb, and too much gas gets in, and the mixture is too rich, and you wont run. On a maxi, if your Carb gasket (the big one) is leaking, it will cause the float to not float all the way up, and it will flood the carb. A leaking gasket will also cause a loss of vaccuum in the float bowl, and too much gas will be sucked up into the carb.
You are right about replacing stock parts, however, some stock parts go bad. the Original Maxi had a plastic, hollow float. This plasic gets old, and breaks down, and leaks. this causes the float to no longer float. You can get a new one which is made of Foam for prety cheap. they still make them for this Carb. Someone else will know where to get them, start a thread to find the best place. The foam will always float, and never get gaslogged.
You will notice a small black button on the side of your carb. this when pushed in, will push down your float, so the gas can pour in. With the petcock open, and gas flowing, when you press, and hold this button down, does gas come pouring out the carb? Does it leak any more than usuall, or does it make no difference? Gas should come out of the base of the button actually.
If gas pours out when you hold the button down, that means that youre float is working, and preventing gas from entering the carb when it is full, and floating. If it makes no difference, and just leaks anyways, you proboly have a float problem. Replace the float. I know you can get a whole Carb rebuild kit on ebay for around $40.