Lexmoto xtrs 125 1999/2000 model badly vibrating in second gear

Hello all I'm totally new to all of this, I've been riding around on a scooter for a few years and have finally made the move to get a licence. So I looked round for a cheap 125 geared bike and found a lexmoto xtrs 125 for 200 quid, thought this will do ( local instructor told me I cant take direct access until I've ridden a geared bike for at least 6 month ), any way everything is perfect with the bike apart from it vibrating in second gear, not so much at low revs more mid to high, it vibrates in all the other gears, but second is ridiculous. so at the end of all that has anyone had this problem or any ideas to what the cause is, thanks

Check ALL the bolts. Old chinese bike's engine mount bolts are ALWAYS loosen.

I was told get a front sproket with an extra tooth and also do the above my clutch cable came loose because of this