Dear Khan garh sb.
First of all let us know either your bike's ignition system is on point or you have converted into CDI?
If point then as FC mentioned most probablly the timing problem.
i have also changed into from 6 v to 12v. thanks God that i didnt convert it into CDI (remebering the thread from Archon:) ). dont now i will change it in future or not but i think its ok at point. though there are some draw backs.
i also have CD185 and i also spent lots of time, in which i some how get fooled by mach/electricians but not know little bit. or you can say now bikes are working ok
in such bikes most important thing is electric system. such strange problems mostly related to electric side.
regarding cd185/200 you will listen 1001 stories but mostly are from stupid jahil nakamay mech/electricians.
mostly handle the matter on the basis of either tuka or little bit experiance seldom have knowlegde of electricity basics, for electricians, and machenical working for mechanics.
so dont rush for solving the problem, read as much as from net to know how things work. so that there will be less chances that you get be fooled from mechnics and electricians.