Trouble starting Yamaha TT600R

[TT5 Matt]

i ad a tt600l [what a lemon] but they do have a low/high speed pick up on them that sometimes causes trouble, you could check the pick up to rotor air gap using plasterseen, as others have said check the flywheel key for being sheered or just take the whole system off and send it to steve at better bikes in adelaide to test on his test bench. as to your after market cdi it sounds like theres something wrong with the advance curved they have programmed into it if its kicking back sooo bad on your mates easy starting bike. good luck with it and let us all know the outcome when its sorted. the tt/xt600's base timing is non adjustable as well

[tymes]

Def check that flywheel key. Valve clearance ok? Remove the ignition coil and clean its mount to earth and clean the wiring earth connection with sand paper. Maybe disconect the kill switches from the wiring harness to try it. Check the plug cap conection where it screws into to the ht wire, usually a good idea to trim about 10mm off ond re-seat it . Close the gap up on the spark plug a bit (is it a new plug?). If you do these one at a time you can at least discount any of them at no cost.

Also backfire can be from a lean fuel issue. Carbies clean?
Kickback sounds like a spark problem