With regards to your comment on learning how to weld via a cafe racer project, you really need to practice a LOT of welding before you attempt ANY welding on a motorcycle. There's not much on a motorcycle frame that isn't structural for the most part and even if you're just welding on a mounting bracket, you're still welding it to a structural part of the frame and you need to know how not to muck it up.
If you want to learn how to weld go get a flux core wire feed welder and make a metal sculpture or weld up some gates or something. Have a look at YouTube for some beginner tips then keep practising until you are confident your welds have good penetration / integrity.