Modern Vespa

Just bought an 08 piaggio bv 200 from a youngster that told me all that was wrong with it was the starter. Replaced starter, still, nothing. One click. That's it. Found out the motor was seized from sitting and the starter wouldn't turn the motor. Changed oil, oiled up top of where starter gear goes, and got the thing to turn over. Now it starts fairly easily, but I have a loud knocking sound. Checked gear oil and it barely showed on dipstick. This bike only has 500 miles on it, and seems to be in great condition. Motor starts very easily, but that noise worries me. If anyone can help

It's highly unlikely the motor was seized from sitting. More likely it was sitting because it was broken. Where is the knock coming from?

The gear box/belt area

Variator, belt or rollers given time scoot has not moved

I like the thinking here. I'd also give the roller between the variator and the clutch the stink eye. I've heard the bearing in that knock before.

What's the frequency? Does it match motor or wheel revolutions or neither?

Frequency is constant. When I press the starter switch, it makes a really bad grinding sound but wants to turn over if I bump it lightly. Had it started and made that knocking sound and it's a loud knock. It's an 05 with a little over 500miles. My guess is it sat a long time. It's frustrating

Oh and the wheel barely spins, even with giving it gas. When it does start, it starts with just a light touch of the starter switch, the engine seems to run smooth.

Well one thing is for sure do not try to ride it on 16 year old tyres and a 16 year old belt it could be very dangerous, have you looked at belt and condition it is in.

Yeah, sounds like you need to pull the trans cover and take a look. Hopefully you will find something as the alternative is your motor is toast.

It is possible that it's your crank bearings. When you pull the CVT cover, belt and variator wiggle the crank shaft, if you have movement bad crank. If no wiggle then something else. I wish you luck.