[NOW FIXED :)]

So today I got back to an old project - a 125cc Chinese scooter (Wangye F1 according to the website). After a few miscellaneous repairs, like a snapped speedometer cable and a dead electric start, I moved onto fixing the oil leak properly with new gaskets. Long story short, it took ages, since I broke a part and stripped a thread in the engine block. Now, it's pretty much back together with new (tampered) gaskets, new oil, all cleaned, the works.

There's an issue though. I finally adjusted the valves, and the scooter went from easily turning over but with no signs of firing, to struggling to get past TDC (presumably) and I ly completing half or maybe a full turn. The compression seems to have jumped up quite a lot. Without the spark plug it spins really easily.

The battery reads a shade under 12v (11.98v), which I know is really low, and likely the real issue, but would there be anything else that could cause the problem?

It's my first scooter and one of my first engines I've worked on properly, so any help is appreciated :)