Very Strange Starter Problem, KZ750 twin

Hello All,

I've been helping a friend of mine with his 1978 750 twin. It's really nice and nearly 100% original including the paint. We have a weird problem though.....it won't start with the electric starter. It starts on one or two kicks but won't fire with the starter. It turns over quickly and smoothly...not a mechanical issue. I can't remember for sure but I think we checked for spark while the starter was cranking and it looked OK. Any ideas? I'm stumped....

Thanks

If the battery is even a little bit low it can cause that problem. My KZ650 will start on 1 or 2 kicks sometimes even when the electric starter won't fire it up. This usually happens if the bike has sat unused for a couple weeks (sometimes less) even though the starter will spin the engine just fine. I suspect the energy used to spin the engine leaves too little juice for the plugs. As a test, you may want to try fully charging the battery and try starting it again to see if that helps. Ed

That was my first thought too. The motorcycle has points which might take more power than an electronic ignition at startup? The battery seems really strong but I'll dig into that a little more.

I wonder it it's common on the 750's. On any of my 650's or 1000's, I've only seen it happen if the battery is too low to crank the starter. I'm guessing if the engine won't start unless the battery is really, really charged up...then something else is probably contributing to the problem. Maybe a bad connection to the coils, weak condensers, etc...? Maybe the famous "coil mod" would help?

It is not the ignition system that causes the voltage to drop, it is the starter motor.
A good test is to put a voltmeter on the 12V wire leading to the coil and press the starter button. If it drops below 10.5 - 11.0 volts, the coils may not have enough energy to fire the plugs enough to start the engine.

Make sure all the starter cables are clean and attached securely, expecially the ground. Also on these bikes the grounding cable goes from the battery to the engine then the strater is grounded to the engine via it's mounting. Make sue the starter has at least one good clean and solid ground point. I have had the same symptoms you are getting with a good battery but then found out the voltage drop was huge whenever I hit the starter button. Turned out to be the resistance from the weak ground.

Great ideas guys, thanks.

Sounds like it could be the starter clutch; a common fault on this bike. Mine was the same, starter spins but it won't fire. Check that out. Good luck.

+1 make sure the starter clutch is good and the engine is actually cranking over.

If it is, it might be a weak coil. When the battery cranks the starter, it typically drops to about 9V. If the coil is marginal, it might not want to start. Measure the battery voltage with a meter while cranking the starter. Under about 9.5V usually means the battery is tired.

Another problem: most of the US bikes have the lights on all the time which throws an extra big current load on the battery when it's trying to start. I rewired mine to disconnect the lights when the starter cranks, extends battery life makes it start better. A new coil also perked it up.

78 model 750 twin has an on/off light switch on the right switch pod.

Make sure the points are good and replace the coil.

+1 on the new coil. $36

www.z1enterprises.com/ItemDetails.aspx?i...zuki&item=EM24-72451

I forgot we'd only need one coil....I'm used to the 1000's needing two. I can't wait to try some of this stuff. I really appreciate all the input....this site is awesome. Here's the only picture I have of the motorcycle...has my friends in it too....can't see the bike very well but I think it's the same as Steell's?