Testing Coils

I've taken off the coils and bought a Multimeter. I would like someone to tell me how to test the coils to see if they're good or bad. I checked the shop manual and it's Greek to me since I'm electronically challenged. A way simple instructional would be ideal.

Hi.
Re testing coils. Page 241 of workshop manual. If not to hand states that primary winding should read with meter set to x 1 ohm and the reading should be between 1.2 - 1.9 ohm They are the cables that feed the coils. secondary winding with meter set to x 1 k ohm should read 12-18 k ohm. they are the HT cables to plugs. They do say that you need the original kwack meter to get a true reading as most off the shelve meters do not give a true reading.
If your thinking that the coils are the problem, take a look in the FAQ section on the site. Still working on mine re intermittent spark and doing my head in and have done the coil conversion :woohoo: .

I read the FAQ and it talks about everything but how to check with a digital multimeter. I'm afraid I'm not familiar with electrical stuff. Simple instructions are good if anyone has the patience to explain.

I can see your dilemma if you're not familiar with the internal workings of an ignition coil. The manual expects you to understand that if you're going to check the coils with a multimeter. So here's a brief explanation and I hope it makes sense.




This is a very simple schematic of a coil. The "Primary circuit" is the one half of the coil where the 12 volt dc is energized across creating a magnetic field inside the coil. When this circuit is broken (or opened) the magnetic field collapses around the primary windings and the secondary windings inducing a current into those windings. Because of the relationship of the number of turns in the primary windings to the number of turns in the secondary windings, the induced voltage onto the secondary windings will either be higher or lower than the primary voltage.
When looking at the simple schematic, the primary "circuit" is on the left side. One of the leads on the coil which is pink in our case is the ground side of the primary winding. The green wire is the positive side of the primary winding. So if you put your multimeter across the pink and the green wires you should have 1.2 - 1.9 ohms.

Now lets talk about the secondary circuit. Back to the schematic, the secondary winding is on the right hand side. Inside the coil one end of the secondary winding is attached to the ground side of the primary winding which is attached to the pink wire. the other end of the secondary winding circuit is the high tension lead that attaches to the spark plug. When the primary field collapses onto the secondary winding the high voltage is induced into the secondary winding and then down the high tension lead jumping the gap across the spark plug and returning to ground. So take your multimeter and stick one lead into the spark plug cap and the other lead onto the pink wire and measure the resistance. According to the manual you should read 12,000 - 18,000 ohms (or 12K Ohms - 18K Ohms)

Let us know what you find.
KB

You're great, many thanks for your simplified answer. I'm getting it although this stuff really doesn't interest me. But it costs me money so I'm a student right now.
I tested the primary side and got 1.7 on each coil. That's good I guess. I tested the secondary side and got no readings at all from any coil. I took off one spark plug boot and tested it for continuity and got a reading of 5,000 ohms so the wire is good.Does this mean my secondaries are all fried? WTF!!??? Wouldn't this prevent the bike from even starting? It was starting and running fine but would quit after 10-15 minutes until it cooled off.
I appreciate your patience.

I take it you remove the spark plug cap from the wire and checked the wire and found 5K ohms, but when you checked with the cap on the wire found and open circuit? 5 K ohms on the wire itself would be about right since there should be a 5 K ohm resistance in the spark plug cap as well.

The secondary winding is inside of the ignition coil. If you measured a low resistance it would indicate a shorted coil probably from being overheated. Overheating can cause the insulation on the secondary winding to fail and then the winding wire will have a short circuit in it.

There are several options for the spark plug cap. Some have no resistance, some have a 5K ohm resistor in them, some have a 10 K ohm resistor in them. NGK offer all 3 types. Not knowing which ones you have, it's a bit of a crap shoot.

One of the most common problems with the spark plug caps that screw on to the wire is that they can come loose after a while and then you have an open circuit between the cap and the wire. Simply cutting a 1/2" off of the wire and screwing the cap back on can remedy that problem.

The other thing that you could check is the continuity in the spark plug cap. Use your tester again and check from the screw end to the end that goes over the spark plug. You should see 5K ohms. If you don't, you could take the cap apart. Inside the end that goes over the plug if you look inside, you'll see a brass fitting that engages the sparkplug. In the end of that should be a slot for a blade screwdriver. If you remove that fitting under it should be a resistor about 1/8" in diameter and about 3/8" long and behind it should be a spring like out of a ball point pen. Needless to say all of the parts should be free of corrosion and the spring should be under compression when the whole thing is together. for the record, the stock caps won't come apart but I know the NGK's will.

Bottom line if the spark plug caps are toast, just buy new ones with the 5K ohm resistors in them and be happy you found a problem.

Anyway, I'm keeping an eye on this one and will answer your questions as best as I can.

Feel free guys to churp in on this post. The more the merrier I always ay.