Well Mahmood its sad what happend but u didnt check the bike when u bought it? i mean engine main problem thi u should have checked.
Mera mashwara yahe hai ask some friend or relative who have been using bikes and us ke help sa theekh karwa lo we have ADIL here i am sure he can help you also Malik and Fahad but these guys are not around these days.
Your bike needs an engine overhaul and go to some proper authorized Honda mechanic.
BTW whenever ur getting this job done of engine make sure u buy original stuff and ask mechanic to fix the engine infront of your eyes.
Baki if you can find a CD70 engine that will be fine as well but if this one can be fixed cheaper than its better to ge it fixed.
And it wont effect price of your bike as long as the mechanic does a good job.