I have changed my first oil on 500 km and then on 1000 km..because mechanic have recommended this.. Yes tappet were loose and tik tik sound was coming from the engine.it is normal ...after first tuning this sound is gone..now sound is very compact..but when i drive my bike very fast on above 80..then little sound is changed and when engine is cooled it become normal...so you dont worry about tik tik sound..it will be fine...in sohc engine it is normal.
And my mechanic is very good..on first tuning he did'nt touched my carborator setting...he only did these things
1-cleaned the air filter
2-tighten the tappets
3-cheked the chain,clutch,Race wire and cleaned the plug.