Italika D150 Sputters and Dies - Please Help

[Nikibahama]

While I have an extensive background in Automotive maintenance/mechanics, I am new to scooters and know next to nothing about carburetors (other than them being a pain in the ass).

I have a D150 (150cc) Italika 4 stroke scooter. Months ago it began sputtering and dying. I'd go 100 feet and it would die. It would take forever to start again, go 500 feet and die, etc... I drained the gas tank, drained the fuel lines, replaced the fuel lines, replaced the fuel filter, blew out the carburetor with carb cleaner, re-assembled everything, filled with fresh gas and voila... she was back up and running like new. I hypothesized there must have been water in the gas somewhere, but here we are several months later and it's back to the same sputtering and dying garbage. I drained the gas, not a drop of water in it...


I drained gas from the drain tube that comes off the carb and hangs by the rear wheel. Once drained the moped started up and ran again for a few miles. Then it started sputtering again and I repeated... ran again for a couple miles. Every time I repeated this, it ran for less distance. Some guy passing by says "put it on the stand, it will start", so I put it on the rear stand (instead of kick stand) and it starts... No idea what the stupid stand has to do with anything, but thought I'd mention it. Put it back on the ground and it just turns and turns without starting (or starts after a minute of trying). So I put it back on the stand and it starts and begins sputtering. I disconnect the fuel feed line from the carburetor. Now it runs like a beast. Revs up, redlines, holds there, keeps going... runs for a minute straight without fuel connected. Re-connect the fuel line and the thing just sputters and dies. Spark plug is black so we're obviously running rich, but this is a stupid simple system... gravity drain fuel with a vacuum-controlled valve that then passes the gas through a filter and down to the carb. There is no fuel pump here where I could possibly be "pumping" too much fuel into this thing, nor have I made any adjustments to the carburetor (it's factory). Can someone please help me understand what the hell is going on here? I can rebuild an entire 8 cylinder motor in my garage but some stupid non-pumped, gravity fed factory carburetor with less than 1500 miles on it since new, is constantly giving problems and running rich without any excessive fuel pressure or force? I'm at my wits end with this stupid piece of s___.