plugs firing question.

I have a 81 KZ750 LTD that I have been rebuilding over the last several years. I finally finished rebuilding the engine and fired the bike up for the first time 2 nights ago. At that time all 4 plugs were firing as all exhaust headers were getting very hot. Now, I went to fire it up again tonight and am not getting spark out of 1 and 4 plugs. Tried the plugs on the 2/3 coil and they are working. Coil is in pretty good shape, no cracks or anything. The only thing that is really different is that the battery is completely dead. Both nights I started her up I was jumping it off a car battery. The first night I could take off the jumper cables for a minute or 2 before the battery would die, tonight it dies the second the jumpers are removed. Could the battery being effed cause one of the coils not to fire or should I be looking at the coil itself.

yes you need about 10.5-11 volts to fire the ignition properly so go and get a new decent quality battery and try it again.

Thanks for the quick reply timebomb. gonna pick one up in the morning. hope that is all it is because i've been off the road for two seasons now and i am going crazy waiting to get back out. supposed to be a georgeous day tomorrow too.

Make sure all the ignition related electrical connections are clean and tight. Any green crud is corrosion and higher resistance. Check the heavy gauge battery cables going to the starter motor,starter solenoid for tightness and the ground cable going from the Negative (-) battery terminal to the engine mounting bolt.

looks like it is the ignition coil. new battery didn't solve the problem. I took the working coil and connected it to the other hookups and got spark from the plugs. time to hit the salvage yards i guess.

Was ohm check done on the bad coil, primary and secondary windings? Might be a bad plug wire or bad plug cap or bad connection between wire and cap.

Good Luck!

ok, not the coil. I went back and double checked everything and cannot get the confirmed working coil to fire on the 1/4 hookups. Anything else I should look at before rewiring? I got a new battery, connections are clean and ground is connected.

Anyone know how difficult rewiring this would be?

I'd disconnect the primary wires to the coil(smaller wires) and using a multimeter set on OHMS check to see if the coil checks good, it should read 2.5 to 3 OHMS. Any less or no reading I'd say the coil has failed.

Suitable replacements can be bought at www.z1enterprises.com I'd also replace the sparkplug leads as they can break down with age and heat.

I've replaced the leads and have tried another coil I found earlier today. still no good. The suspected bad coils will get spark when connected to the 2/3 lines.

Where outside plugs aren't firing, let's do some step-by-step testing.

With ignition switched ON (engine not running), is battery voltage reaching the coil (that would be the coil with wires to the outside plugs)?

Test result should be --
Same as battery voltage
Or something less than battery voltage
Or no voltage at all :pinch:

Good Luck!

I'll have to get a multimeter and test that later this week, right now I'm off to work.

problem is now solved. there was no current on the blue wire coming out of the IC igniter. Grabbed a new igniter from the local salvage yard and now she is firing on all 4 again. The only problem now is that the igniter came out of a kz550 and it had a different connector. My original had a female connector where this one had a male. I ended up just cutting the connectors and soldering everything direct.This seems to be working good, but now the cables are not long enough to fit it back into it's mount behind the fusebox. There is lots of room for it under the seat, behind the battery box, the only concern I have is with it rattling around too much. It's in between the frame and the rear fender and I used electrical tape to secure it. That's really gonna bother me until I can get enough time to rewire it.