Dual fire high output coils

My Dyna 3 ohm dual coil tested at 2.9 ohm and the red boyer box it was fed by stopped working after 20mins on hot summer days, waiting 5 mins ignition off gave me another 20 mins run time. I swapped it for a 3.0 ohm Harley type twin coil and normal service was resumed.  So if given the choice I would go slightly higher than the lowest allowable ohms which for the red boyer box is 3 ohms.

I used the 5 ohm one from Norbsa (www.norbsa02.freeuk.com/goffyelectrex.htm) with a Boyer and it gave good sparks.

"I'm trying to locate and purchase Crane, Dyna, Andrews style High output single fire dual output coil for my 1973 Mk2a 850 which has B Bransen ignition. "

Since B Bransden  is a company brand, and not a particular type of system. How can anyone advise when no system type is declared??

The Boyer Bransden Micro MKIII and Micro MKIV electronic ignitions are built for the original Lucas 17M6 coils which are rated at 1.7 to 1.9 ohms each.

So as a pair wired in series that will give you a target of 3.4 to 3.8 ohms.

Your dual output single coil should be rated the same.

You can get 4 and 5 ohm models which will be absolutely fine in your application.

Don't go for the readily available 3 ohm model - as pointed out already, your ignition will burn out pretty quickly.

Here are a couple of options:

https://www.arhcustom.co.uk/product/drag-specialties-dual-fire-ignition-coil-in-black-4-ohm-electronic-ignition-10-2028

https://www.arhcustom.co.uk/product/drag-specialties-12v-mini-dual-fire-ignition-coil-5-ohm-electronic-ignition-dual-fire-10-2041