Today I install a TB 88cc kit, and a Hotcams cam chain on a XR70. This video should cover similar models XR50,CRF50, and CRF70
https://www.ebay.com/itm/171510587419?hash=item27eed3e01b:g:71QAAMXQjq5Q-f14
https://www.ebay.com/itm/393383919034?fits=Model%3AXR70R&epid=171172727&hash=item5b97823dba:g:aLMAAOSwRrlgvaB9
https://www.ebay.com/itm/372941475927?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D15da159378114b4da39d2154980f319e%26pid%3D100675%26rk%3D14%26rkt%3D15%26sd%3D232230619829%26itm%3D372941475927%26pmt%3D1%26noa%3D1%26pg%3D2380057%26brand%3DHot+Cams&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A3c006f64-f4c8-11eb-9896-2e5956c3797e%7Cparentrq%3A0ee73b3417b0acf09832f8f6ffefd2ec%7Ciid%3A1