Topic: Coils to plugs wiring

[FondaHonda]

Sorry for being a dumbass but I have a question. I have a 1972 cb750 I recently bought. The plug wires were in bad shape so I bought a used set in better shape. The newer set has numbers 1 - 4 on the wires at the plug end, but it doesn't match the way the old ones were wired. I think 1&4, 2&3 were reversed. I have a wiring diagram but I'm not sure how to interpret it. Looking at the 2 coils as I sit on the bike, how should they be connecting to the plugs? It has been fouling plugs which may be another matter, but I want to make sure I have it wired right. Thanks for your help.

[Jonesy]

You can have the coil for 1 and 4 going to plugs 1 and 4, but that doesn't mean wire #1 HAS to be on plug #1. These bikes run on a "wasted spark" setup. Both #1 & #4 plugs fire at the same time, since one is on the compression stroke (in which case the plug will ignite the air/fuel charge) while the other is on the exhaust stroke (in which case the plug will be sparking into a cylinder full of exhaust gasses and do essentially nothing). Cylinders 2 and 3 work on the same principle. So, plug wire #1 can be on plug #4 and vice versa, and the engine will still run fine.

The wires that must be properly connected are the ground wires connected to the points. The blue wire triggers the coil for cylinders 1 and 4, while the yellow wire triggers the coil for cylinders 2 and 3.

Both coils are exactly the same, so in theory (for example) you could use a "1&4" coil for cylinders 2 and 3, provided it was triggered with the yellow wire (despite that it has a blue wire coming out of it).

[FondaHonda]

Thanks for the reply & info. That explains why I didn't notice any difference when I switched the wires. This is great info, I really appreciate it.

[fdbrat]

Does this apply to a cb650 as well. I just wired in the engine swap and im not sure if the coils are wired right.

Where does the black and white wires go . Do they go to the neg terminals or the positive on the coils?

Im at a loss.

Thanx

[w1sa]

The ignition electrics on the CB650 are different in that, instead of a points ignition system, it incorporates a 'pulse generator' and  'spark' units.

The wiring colour codes for the ignition coils are the same.
So, Black/White is the switched battery  to  + ve at each coil. Blue to 1-4 coil -ve and, Yellow to 2-3 coil -ve

Here is a link to CB650 Manual and Electrics/wiring diagram
http://cosky0.tripod.com/

[Alan F.]

Although it didn't supply the answer, I'll compliment your use of the search function FDBrat, not everyone will actually search for their own answers before asking.
-A

[fdbrat]

Thanx I do alot of searching. Well i got the bike running and now ill be off toanother thread on carbs.