TOPIC:

I bought this '78 (built late in 78, looks more like a '79) 650SR last Fall and am just now getting around to trying to get it running right. It does now start good and runs but it doesn't run right, very little power. It doesn't seem bad enough to be missing on two cylinders but I pulled the new plugs I put in last Fall and numbers 3 and 4 don't appear to have ever fired while I have a nice tan burn on the number 1 and 2 plugs. Next I checked the coils and I have no continuity between the secondary wires through each coil. I'm thinking I have one bad plug wire per coil since the effected cylinders are each on a different coil. It doesn't appear that the plug wires can be removed from the coils. According to the manual there should be 4 ohms of resistance between the primary leads and mine read just over that. Z-1 only shows 3 ohm "Dyna?" coils. What can I use to replace these coils and plug wires and where can I get them. If anyone has any other ideas or thoughts, I would sure appreciate any help.
Thanks, Tom

When my KZ 750 coil went bad, I lucked out and found one on ebay.

Be careful substituting coils with a lower primary resistance becaust that increases the amount of current the ignition draws when running. IMHO, a 4 Ohm coil should be replaced with a four Ohm coil, not a three Ohm coil.

I'll see if I can find a place with discount OEM coils.

Here's one on ebay:

cgi.ebay.com/ebaymotors/1978-Kawasaki-KZ...dZ1QQsspagenameZWDVW

That's what I figured. I am watching the one you mention on E-Bay, would like to hear from him that they actually work and not just "sold as is". If you can find a source for new replacements I would rather go that route. The bike has only 14,000 miles on it and could be a nice driver to save some gas. Besides that, I bought one of these new (when I was 8 years old) and then bought a used '79 in 1986. I just love these things and just want to get it running decent to ride a little take myself back. Thanks for your help !!

Tom

Next I checked the coils and I have no continuity between the secondary wires through each coil

There should be 16k-19k ohms resistance between the two spark plug wires (secondary) on each coil.

The KZ's use a wasted spark system, one coil fires two plugs. One plug wire is hooked to one end of the secondary, and the other plug wire is hooked to the other end of the secondary, and the current flow is from the coil, through one plug wire, jump the gap on the plug, across the head and jump the gap on the plug, then back up the other plug wire to the coil. There is a diagram in every KZ manual I have (KZ650, KZ750 twin, KZ750 four, KZ1000/1100) that shows that very clearly.

Keep that in mind when diagnosing ignition system problems, it will help immensely

Think of it as a complete circuit, break it anywhere and the whole circuit is dead.

I was going by the Clymers Manual that I have for the bike. It shows how to check resistance in both the primary and secondarys and what the readings should be. I have good readings on the primarys but no reading at all (open circuit) on the secondarys.

steell wrote:

The KZ's use a wasted spark system, one coil fires two plugs. One plug wire is hooked to one end of the secondary, and the other plug wire is hooked to the other end of the secondary, and the current flow is from the coil, through one plug wire, jump the gap on the plug, across the head and jump the gap on the plug, then back up the other plug wire to the coil. There is a diagram in every KZ manual I have (KZ650, KZ750 twin, KZ750 four, KZ1000/1100) that shows that very clearly.

I don't know about the other models listed.

The coil on my 1979 KZ 750 twin is not wired in that way. I have the FSM in front of me and here is how it is connected on the wiring diagram (see drawing below which shows connections):

There is one and only one "high voltage tap" on the coil's secondary winding supplying both of the two spark plug wires. It is shown as a single internal connection point with two heavy black (plug) wires coming out to go to each spark plug.

Each plug wire goes to the spark plug, and the other side of the plug (across the air gap) is ground. This is why I have always thought the two plugs were in parallel from the coil's high voltage secondary winding tap point to the plugs and then to ground (across the plugs).

The other (low voltage) end of the secondary winding is tied to +12V, as is the positive end of the primary winding. My schematic shows those two winding ends tied together inside the coil and come out as a single yellow-red wire which connects to +12V.

The negative end of the primary winding comes out as a blue wire to the points which ground it when the points close.

Here is how it is shown to be connected in my FSM. As shown, the spark plugs split in parallel off the high voltage end of the secondary winding. Each spark plug branch has a separate path to ground.

The diagram reinforces the fact that I should have continuity between the two plug wires. Since I do not, then at least one plug wire on each has to be bad since numers 3 and 4 (one from each coil) are not firing. It would seem to me that if both COILS were bad that it wouldn't run...?

So, does anyone have a source for the coils/wires ?

Thanks to everyone for their input !

Tom

Tom, try removing the spark plug cap, and cut a 1/4 inch or a bit more off the end of the wire. Then put the spark plug cap back on while turning it clockwise.
Sometimes the connection gets bad between the cap and wire, and needs to be renewed.

Hey thanks, I'll give that a try - it makes sense ! I'll let you know what happened. tom

twjoyce wrote:

The diagram reinforces the fact that I should have continuity between the two plug wires. Since I do not, then at least one plug wire on each has to be bad since numers 3 and 4 (one from each coil) are not firing.

I like the suggestion of taking off the plug caps. Then, measure the resistance between the center conductors of the wires to check continuity.

The reason is this: there are "resistor" type plug caps which might have a high enough resistance that they might look like you have no continuity when you are reading the wires on your meter, depending on how high the meter ranges go for reading resistance. The resistance of the caps would be in series with the wires.

And the idea of pruning the wire back a bit to get fresh center conductor is a good one.

twjoyce wrote:

If you can find a source for new replacements I would rather go that route.

Thanks for your help !!

Tom

I had found a site that was selling NEW replacement coils for the Kawi twins for a cheap price (I think about $50) but now I can't find it. I had it bookmarked on my work computer but I no longer have access to it, and I was locked out of it the day I departed so I couldn't download any information.

I looked for the site last night and couldn't find it. If I ever do see it again, I'll post it.