What's this sound like to you?

I just recently bought a 1979 KZ750. Its a sweet looker, not a show bike, but will make a great daily rider this spring.

Its having a little trouble starting. I've read a lot about the starter clutch problems that plagued this bike. I'm not sure if that's what's going on here or if it is something else.

Take a listen and tell me what you think.

This is with a freshly charged battery, but on a very cold morning (in the 30's).

When you hear it sort of wzz... wzz... wzz... then catch, I've got my thumb on the starter button the whole time. Is that normal?

Also at about :07 seconds, :16, :26 :30 and :33 seconds you'll hear what has me wondering about the starter clutch.

I plan to pull the starter clutch, install a rebuild kit and put some locktight on the starter clutch allen screws just to be on the safe side after reading the article over on www.kz750.com

What I'm wondering is if that's not all I've got going on here. I don't particularly want to have to pull the generator cover off twice if it turns out I've got starter problems too.

What does this sound like to you?

I'm not familiar with the twins and the starter clutch issue, but it doesn't sound like the starter clutch IMO. If it were, then the starter would be spinning faster. Sounds like the combination of weak battery or starter with cold weather. You said that the battery was recently charged, so assuming that the battery is good, then I would look for dodgy electrical connections next. Watch the first part of my video here. It sounds the same to me as your bike starting. I'm using a known weak battery to start this bike in the video:



Pay attention at 0:30 for the hesitation when it starts. Sounds like your audio to me. If it were a cold day when I tried this, the bike wouldn't have started, but I got away with it since it's about 80F in this video.

BTW this battery will take a charge and get to 12VDC+ but it doesn't have the load capacity to reliably start the bike in cool weather.

Doesn't sound like the starter clutch... You would hear the starter motor spinning without engaging if it was the clutch. To me, it sounds like too little current getting to the starter motor. Maybe you could try another battery, or check the starter motor windings.
Best of luck,
Grant.

I'll take the battery to a local auto store and have it tested. I'll let you know what I find out.

Thanks!

Grantl wrote:

Doesn't sound like the starter clutch... You would hear the starter motor spinning without engaging if it was the clutch. To me, it sounds like too little current getting to the starter motor. Maybe you could try another battery, or check the starter motor windings.
Best of luck,
Grant.

x2


just needs to be turning better(stronger/faster) and ready to start imo....twins have a different sound...it is a twin?

Hi Topper, It sure sounds like a faulty or undercharged battery. Check the specific gravity of the acid in each cell to see if they are up to specs, you may have a couple of weak cells. A good battery is essential to start these KZs. Just my 2 cents worth. My Kz 650E sounded the same when the battery was bad . The starter clutch sounds solid. Bob

It's about 99% likely it's a weak battery. Just because it's fully charged, doesn't mean it can cut the mustard. measure the battery terminal voltage then crank the starter. If the battery voltage drops below about 9.5V, the battery internal impedance is too high to deliver enough cold cranking Amps.

A bad starter may be drawing too much current, but that's much less likely than a bad battery.

trianglelaguna wrote:

....twins have a different sound...it is a twin?

Yep its a twin.

You all nailed it. The local auto store tested the battery and it was no good.

Got a new battery and I'll try it out tomorrow.

So here's the bike with a new battery.

Listen with fresh battery.

Better, but not quite what I was hoping for either.

Now its 32 degrees (farenheight) out there, so maybe I shouldn't worry. Maybe this'll be fine come spring if I tend to the battery over the rest of the winter.

What do you think? Is a starter rebuild in order?

I'd pull the starter and inspect for worn commutator and brushes.

Starter Motor Rebuild Kits
www.mawonline.com/newsite/rick_s_motorsp...-starter_brushes.htm
www.cyclewareables.com/pages/street_star...kits/startmtrkit.htm (not sure if website is viable)
www.psep.biz/store/mitsuba_starter_motors_page_2.htm

What weight oil are you using?

+1 on MFolks advice.

Not sure. She's new to me, had her less than a week. Haven't done an oil change yet, but will before too long.