>I have the original 12 volt coils fitted.
I am told by an electrically minded friend that I should change the coils to 6 volt.

Theoretically, two 6V coils connected in series should produce stronger sparks than two 12V coils in series, however, two 12V coils can often prove satisfactory as long as the engine isn't high compression or highly tuned. Unless you have experienced any repeated problems such as bad starting or fouled plugs then little or nothing may be gained by changing to 6V coils. Easiest way would be to borrow a pair of 6V coils and try them.

>The 12 volt coils draw too much current.

Unless they happened to be connected in parallel, then they shouldn't (whether 6V or 12V, coils should always be connected in series with the Boyer ignition, see Boyer diagram).

http://www.boyerbransden.com/pdf/KIT00052.pdf


>The bike has a solid state reg. and rectifier fitted along with a 3 phase stator.

I would have expected a 3-phase alternator to be capable of keeping up with the demand unless the bike was ridden slowly for long periods.
Rotors eventually lose magnetism which reduces alternator output so unless there's a charging problem maybe its time for a new rotor?