Need ID help

I sometimes can't tell with the motor in my hand : (

That straight up spark plug is oftentimes a 48cc tho.

big thing is if you like it, if so get it

Looks like a 48cc by the way the head looks and
you can be certain if it has 6 mm head studs.

Almost all of the 66 cc motors have 8 mm head studs.

it could be a older 66cc with the strait plug

Looks like a decent build - at that price, it would make a good first bike - work on getting that chain to stop rubbing on the tire and learn some other stuff you'll need to know. After a while, you should be able to sell it for what you paid and make a good decision on starting you own build.

I'd probably buy it, clean it up, then resell it for $400.

there are no 80 c.c. china 2 strokes.
they came in either 66 cc, or 48 c.c., but they call the 66 c.c. an 80 c.c.
not all 48 c.c. engines had the stright up spark plug either (or flat head design). I have a 48 c.c. with a slanted plug (or slant head design).
older 66 c.c. engines were made with flat heads (straight plug) for a long time.
the only true way to tell if it is a 66 or a 48, is to pull the head off, and measure the bore of the cylinder.
or the easy way is by measuring the head studs (6mm studs = 48 c.c. 8 mm studs = 66 c.c.)

In reality, there's not much difference in performance of the 66 vs. the 48.
actually, the 48 c.c. engines rev higher and run smoother than the 66 c.c. engines.
I have a bike with a 48 c.c. on it and another bike with a 66 c.c. on it, and to be honest, my 48 c.c. bike will out run my 66 c.c. bikie.
they are built pretty much the same and they both have the same size rear sprocket (41 teeth).

the grubee gt-4 starfire 66's had 6mm studs, so you can't always go by stud size.

$250 is a pretty good deal for a working, used China Girl. First thing I would do is get some front brakes, then check all the fasteners. (nuts and bolts)

Even if it craps out on you some time soon, can get a replacement engine for less then $100.

Read, read, and read some more. Some great advice floating around.

Also, I find a motorcycle or the like, helmet is much safer as it lets cars know your going faster then a bicycle.

Welcome to the forum and ride safe!