some times my tp magna starts to runs on 3 cyl when its cold can some one help me

Give yur plugs a good clean or renew em.
Check inside yur distributer cap is clean
Give her a new set of leads for chrismas if they are a bit old
Run a bottle of injector cleaner through it if it has injecters or some carby clean if its carb

Then see how she goes. :D