Motorcycle Repair: bsa electrical probs, capacitor kit, compression stroke

Question
Hi John,
I have a 68 bsa spitfire 650 that has an electrical problem, big surprise,eh? I'm having problems getting it to fire on both sides simultaneously. Both the points seem to be functioning properly and by switching coil wires around I can get a spark out of both coils but not while they're both hooked up at the same time, it's either one side or the other. Also, I'm a little confused about the wires attaching to the coils, my repair manuals don't seem to have an accurate diagram of the way they go on. There's  four terminals (prongs) on each coil, two for pos, two for negs.  On the pos side I connected the wires coming from the points but have  three more wires that I'm not sure where to attach them.  These are two white wires (together) and a black and white (or maybe yellow) wire and then the same deal for the other coil.The bike does not a capacitor kit installed. I'm really stumped.  Thanks for any advice.  Best wishes for you and your family.          Scott

Answer
Scott
I guess we need to make a couple of things clear before you have me confused. Number one is that the coils are not going to fire simultaneously. They will fire in sequence, hopefully at the proper moment when each cylinder is a few degrees before the top of the compression stroke.

Number two, from now on, when you disassemble something, no matter how simple it seems at the time, you must tag the pieces to know how they go back together. This is especially true of wires and electrics.

Your coils have multiple prongs, but not all are used. As far as wiring diagrams go, they rarely seem to fit the reality, but if you have a little understanding, they can be a big help if you have the right one. More than once, I have taken a knife to a harness just so I could reassure myself that the wires I was following went where I thought they went.

Your coils should have a black and white lead coming from one set of points and a black and yellow lead coming from the other to a positive terminal. It is up to you to see that the lead is going to the proper coil. Stick a finger in a spark plug hole and turn the engine over slowly. You can feel the compression. The set of points opening on this stroke are the ones that fire this cylinder. Make sure they are wired to the proper coil.

The white wires connect to the negative terminals.
One white wire connects the two negative terminals of the coils to each other. One (white?) wire connects the coil receiving the black/white lead to the ignition switch. One wire (white?) connects the coil receiving the black/yellow lead to the the front brake switch, according to my book.

It's tough to explain all this in written form when there is no physical example around to point at. I am telling you this with the aid of my diagram and a dim memory of the last time I plugged wires on a BSA.  I can't be sure that I have told you all you need to know. And if someone has messed with the wiring before you came on the scene then everything I have told you goes out the window.

But maybe I've helped a little bit.

John