Confirm my suspicion - dying starter motor

I've suspected for some time that the starter motor on my '79 kz750 is on death's door. Can you all help me confirm or refute this diagnosis?

Today
The latest evidence came today. I had just finished replacing the throttle cables, put everything back together, hit the starter button and all I got was a click from the starter solenoid. I pulled the tank off and checked the connections around the coils thinking I might have jiggled one loose. They all looked fine. Checked all the other connectors around the areas I worked, checked voltage at battery and coils. Everything looked fine.

Because I've been suspecting the starter motor, I connected some jumper cables to my battery, touched the positive end to the starter motor terminal and nothing happened.

Put everything back together. Tried kicking it over a couple times. After about two good kicks it hadn't started and I hit the starter button again. This time the starter spun, but weakly. I kicked again, hit the starter and the bike fired up.

Previously
I suspected the starter because I've had intermittent issues with the electric starter ever since I bought the bike two years ago. I would occassionally hear the starter clutch grind, so I pulled it and replaced the springs, pins, etc. even though they looked fine. I also pulled the starter and installed new brushes and ran the armature through the tests in my manual. It didn't do very well, but I'm a noob and wasn't sure I was doing the tests correctly. The whole armature was covered in some kind of red oxidation. I cleaned it up and reinstalled it.

My suspicion
So my suspicion is that the armature itself is failing and that I did perform the tests from the manual correctly after all. Depending on where the brushes are sitting on the armature, I either get enough from the motor to start the bike, not quite enough (causing the starter clutch to complain loudly) or nothing at all. Kicking the bike over a few times causes the starter to turn, rotating the armature and I get another shot at starting the bike.

Does this sound like a reasonable theory to you?

I've been relying less and less on the electric start and focusing more on kick starting, so this would be less of a problem. But I'm lazy and would prefer the convenience of electric start when I want it.

Check the engine grounds (starter to block and system at rear behind kick start arm) for good clean connection.
You might want to check and clean the starter button contacts also.

Good luck, Jim.

I thought the start motor ground itself via it's direct connection to the block. The only lead coming off mine is a positive lead.

It does,
but if the starter mount bolts are lose it can build up corrosion between the block and the starter motor housing.
The system ground completes the circuit between the battery and the engine block.

All the connections need to be clean
battery + to starter solonoid input
solonoid output to starter post
starter body to engine block
engine block to battery -

The 79 750 twin is extra sensitive to battery condition due to starting with the headlight always on. If the starter is not activating, pull the middle fuse from the fuse box (headlight) and try the starter. If it works without any other changes it is probably low battery voltage.

New battery, or
headlight cutout relay (I have don this and it works well).

Good luck, Jim

Thanks for the help Jim. The battery is relatively new (maybe a year and a half old) and I just took it off trickle charge a couple days ago. Pulled it and put it back on charge just in case. Checked the ground behind the kick starter and at the starter motor. All looks good.

I'd be 100% convinced it's the starter motor if it weren't for the fact that I can't kick start it today either. Usually it starts up within 3 or 4 kicks max.

Gonna let the battery charge tonight and start again tomorrow.

Starter Motors
www.nationsautoelectric.com/Kawasaki.html
www.whitedogbikes.com/cat--Kawasaki-Star...-Starter-Motors.html
www.ricksmotorsportelectrics.com/starters.php

Ok, I must have more than one problem here.

Had battery test. It's good. Pulled the starter, hooked to a battery and nothing happened. Pull the starter apart and see that the tip of the spring that holds one of the brushes is broken and not holding the brush down. I was able to bend it and work it back into place. Test the starter with a battery and it spins right up.

Reinstalled the starter, started the bike. It took a little longer than usual to start, but it did fire up. I let it run for a few minutes, cut it off and tried to start it again. No dice.

Now the starter's whizzing away, but it sounds like the starter clutch isn't catching. I put in a starter clutch kit last year when I was trying to chase this intermittent problem down. The kit included the springs, rollers and pins.

Can you guys watch the attached video and confirm that sounds like a starter clutch problem? If it is, then what's left to replace?

On the bigger 4's, any of the parts that interact with the springs, rollers & clutch, should be examined for wear.On your twin, I'd imagine the same thing. Also, what type/kind of engine oil being used? If it's car oil, the friction modifiers in it may be causing the slip problem.

JASO OIL SPECS:
Find an oil that shows the JASO-MA rating on the bottle; there are plenty of them available both dino and synthetic.

The ingredients in oils have changed over the years. For example, today's Castrol GTX oil (and pretty much all other AUTOMOBILE oil) is not the same as it was in the 1980's. Back then it worked great in KZ bikes. But, things have changed. Early AUTOMOBILE oils contained zinc phosphorus compounds (ZDDP) to protect engines from metal to metal contact. This was good for engines, but it was found to be destructive to catalytic converters. Consequently, in AUTOMOBILE oils ZDDP was virtually eliminated and replaced with different chemistry generically referred to as "Friction Modifiers."

These work fine and offer good protection for normal AUTOMOBILE engines. However, today's AUTOMOBILE oil "Friction Modifiers" are destructive to wet clutches. KZ bikes (and many other brands) have wet clutches. As a result of these oil chemistry changes a distinction needed to be made between those oils which are suitable for wet clutches and those which are not.

That distinction was documented by the Japanese Engine Oil Standards Implementation Panel (JASO). JASO developed a number of different oil specifications for different applications. The specifications that apply to 4 stroke motorcycles fall under the "4T Specifications." Within the 4T specifications the JASO MA class oils are specifically formulated for 4 stroke motorcycles with wet clutches.

Using oils that are not designated as meeting the JASO-MA standard may be destructive to KZ clutches. Here's a link that may be helpful:

www.oilspecifications.org/jaso.php

Topper, sounds like the small pin/ key that holds the gear to the housing may have fallen out while you had it apart. Pull it one more time and look for the small piece.
Sorry I just had a look at the parts diagram for yours and had it wrong.
I would look to see if the chain is on correctly and the small chain drive gear is retained correctly by the snap-ring.

Edit: Well I thought I remembered a thread on this, I found it.
www.kzrider.com/forum/4-electrical/47568...start-updated#475918
Have a look and see if yours has this small Key/ Pin to hold the inner Sun gear to the End Housing.

There's no pin or clip on the small gear on mine.

the small Pin/ Key would be inside the starter motor assy. Opposite end to the brushes.
Have a look at that thread from 750steve.

OK, I'll have to disassemble tonight and check that out. My bike sounds exactly like one of his videos. If that little pin fell out it's lost for good. If that's the case I'll be looking for a new starter.