HondaCB650

My bike is not giving a spark, except a tiny one on spark plug #3 so I wanted to check if my ignition coil is ok. I'm not good with electric stuff so forgive me if this is too basic.
If I put the multimeter on resistance (ohms) and I take the reading from the side where the power comes in (left, red arrows), it gives me some kind of reading (around 700).
If I test them where it comes in and out towards the plugs (right, yellow arrows) I get no reading whatsoever on both coils.
Am i testing it the right way? Does this mean they are dead?

forgot the pic

You cant test as you describe in the pic with those yellow arrows as its two different cirquits! You must test that cirquit by grounding one test pin to the ground of the coil. The cirquit you test with the red arrow is connected to the igntion controller wich in turn is connected to the pulse generator.
From where you marked with the lower yellow arrow and to the nearest ground you can check the ignition cirquit.

OK, I will sound like a complete idiot if I ask anything else: I'll get a book about this, you just spoke greek to me! Circuits and grounds and wires are not familiar at all to me and I have A LOT to check and test on this bike!

How little I know and how many things can go weird on one bike?!
Duh!

You ground that coil with the rest of the bike by just mount it on the frame and the hole where the screws goes is the area to ground it! I have used your picture and changed the arrows.



If you check the coils where i have placed the yellow arrows you will get a reading if the coils work.
The primary coil you check by connecting where the red arrows points. The secondary coil you check by connecting where the yellow arrows points. And where i have made a new yellow arrow is the ground to the rest of the bike.

MEHall wrote:If you check the coils where i have placed the yellow arrows you will get a reading if the coils work.

Sorry, the CB650 ignition coil should have no ground connection. The secondary circuit is between the two ignition cable terminals. So the second yellow arrow has to point to the second plug cable terminal. The right arrows are correct for the primary side.

The well known consequence of this fact is the common failure of 1+4 and 2+3 pairs in most ignition related problems as well as the fact that a single plug won't fire when the other plug cap of the pair is pulled.

The function of ground is to close the circuits for both coils.

OK, when I tested by connecting two plug terminals, I have a reading, on both ignition coils. Anyway, I took them to the electrician and he said that they test good.
It looks like I do have a faulty pulse generator (I did ask about that one as well, it had a broken wire) which my friend tried to save. I'll see if I can find a new one.
As always, thank you gentlemen

Well i might be wrong in what is primary and secondary coils but i know at least you wont get any connection from where red arrows are placed and through where the left yellow arrow are placed. It's two different circuits. But how the heck is the coils grounded that goes to the spark plug really? I know at least that in older cars the ignition coil is grounded through the cars boby and to the engine.

I'm sure Volker will come back to explain.

MEHall wrote:Well i might be wrong in what is primary and secondary coils

No, this is correct.

MEHall wrote:but i know at least you wont get any connection from where red arrows are placed and through where the left yellow arrow are placed. It's two different circuits.

Also true.

MEHall wrote: But how the heck is the coils grounded that goes to the spark plug really?

Please refer to page 17-3 of the manual linked below. From both coils, the secondary circuits are closed "by ground" but not "to ground".
In other words for the secondary circuit ground is not identical with one terminal (like for the battery) but just a part of the "cable".
This includes that the plugs of a single pair would fire perfectly if you removed them both from the engine and just hold together their threads.

MEHall wrote:I know at least that in older cars the ignition coil is grounded through the cars boby and to the engine.

These cars typically use an ignition distributor. Different concept.

So odd, the ignition circuits are closed through both spark plugs.
Well so long it works....