Vento Phantom R4I '06 Startup Problems

[IntensiV]

Hey everyone! I'm new here. Sorry for the hefty post. I just wanna be as detailed as I can be. I bought this scooter (150cc Vento Phantom R4I) off a random dude on Craigslist. Didn't know much about scooters or anything automotive before I bought it so of course, I ran into a multitude of problems and now I'm at the point where it will not start and I cannot figure out the cause.

So the scooter only ran for a few days before breaking down. We dove in and found the scooter was running off a car battery. The carb was bad and the air filter was oily and dirty. So we bought a brand new carb and air filter. We also ended up replacing the clutch pulley as the old one practically fell apart when we took it off. Fuel filter was dirty and old looking so that was replaced as well. Upon putting things back together, one of the main bolts that secures the exhaust to the engine broke off so it was quite loud when I was running it.

I rode it again for a couple days before it broke down in the middle of nowhere. Couldn't figure out the problem so I let it sit for a few days. During that time, I switched out the 3 way valve (The air/fuel line one), changed the oil, cleaned the oil filter and changed the spark plug. Still didn't start up. When trying to start it up, it would seem as if it was losing power/slowly dying (Off a car battery, keep in mind). So I went to buy a normal sized scooter battery and boom, started up right away. I drove it around for a bit and all seemed ok. The following morning, I went to start it up and it had the same losing power/slowly dying problem. I thought maybe the battery I bought was too small. So I bought another battery a bit bigger, installed it, tried to start it up and it doesn't even turn over. Confusing. So I put the original battery back in (The car battery) and it started up fine. Confused about the whole thing, but happy it was running again.

Drove it for a few more days before it broke down again. Turned out the CVT belt got completely shredded to pieces (I think the person who put it on didn't make it tight enough somehow cause it was loose looking to me). I took it to a shop where I watch the guy do the work so I know he didn't mess with anything else. He replaced the belt as well as the variator. After that, it rode the best it's ever ran. Hitting 55+ and everything seemed smooth aside from the loud exhaust. I took a nap at a friend's and went to drive it home only to experience acceleration problems now. It would bog frequently around 25-30 mph and wouldn't really let me go any faster. Tried messing with the air/fuel mixture on the carb but didn't have any luck. Eventually, the scooter stopped turning over all together.

So it hasn't been running for a couple weeks now. During this time, I've replaced the CDI, the fuel and air lines, the spark plug cable and discovered there was an oil leak cause I drained my oil and I didn't have much in there...I was thinking I might've damaged the engine if I was running it on low oil. There were times when I would try to start it up and there would be a coughing, grunting-like sound. Dunno if that sounds familiar.

Thoughts? Thank you in advance for any help. My next step was to replace the starter but after reading about the symptoms of a bad starter, I doubt that's the issue.