@smijaz
i have read some where the following quotes:
"Measure the primary resistance of the coil.If it is from 2.4 to 3 Ohm it is a 12v coil i.e it does not need a ballast resistance in series.If it measures about 1.5 Ohm it is a 6v coil and needs a ballast resistance in series of approximately the same value i.e 1.5 Ohm."
and then i measured the primary side resistance of my coil it is 1.5 Ohm from + to - terminal and 2.5 ohm from B to - terminal so i transferred the electrical connections from + terminal to B terminal and if some one have got the simple coil w/o resistance then external resistance could be used.I have measured the value of external resistance and it is found to be 1 ohm so it means its just internal/external issue otherwise resistance is the same.
I think that the manufacturer built the coil for 6v or 9v to reduce the number of winding of primary coil which helps in self induction at high rpm and resistance is implemented to reduce the voltage to the coil.