Starter troubles

Having some electric starter troubles on my '79 KZ750 and am hoping for some advice. (Please don't say get rid of the electric start and just kick it, this is about how to get my electric start working).

Ok, so the full background here is that I've known for a few weeks at least that the starter clutch was starting go. It would occassionally get that marbly, grinding sound these are famous for. I've got the parts for the starter clutch rebuild and was planning on tackling that when it got a little colder. The problem was intermittent so I figured I had some time.

Fastforward about two weeks. I push the starter button and hear the solenoid/relay under the seat click, but nothing else happens for about half a second. Then the starter whines weakly but fires up the bike. I made sure the battery was fully charged, but it still had this behavior. I got 3 or 4 starts like this and then it quit.

Now when I press the start button the solenoid clicks, but the starter doesn't react at all.

I decided to test the solenoid per my manual. I'm getting 12v to the solenoid. When I put my multimeter across the terminals and hit the start button, I hear it click and the meter reacts. With the multimeter in the 20k ohm setting it goes to zero. In the 2000 ohm setting it flickers between 1 and 0.

This seemed like the solenoid may or may not be bad, so I tried running a car jumper cable from the positive battery terminal to the starter side of the solenoid with the clutch lever pulled and everything on. Nothing happened. I tried running a jumper cable from the positive battery terminal to the wire nut on the starter and nothing happened.

I've checked all my fuses, they're fine. I replaced the starter motor brushes about a year ago.

I'm looking for suggestions as to what this could be. If the starter clutch were causing a problem, I'd hear the starter motor trying to turn over and probably more of that marbly, grinding sound right?

Keep in mind that the starter motor is by far the biggest drain on the battery / electrical system. I do not know how many watts the starter on that machine is looking for but would assume it is somewhere between 500 and 900 watts. Remember watts = volts X amps. So if the starter is looking for, lets say 700 watts then the battery needs to provide about 58 amps for the starter motor to work correctly. The starter motor does not care how it gets the needed wattage - if the battery is not at proper voltage the starter will attempt to pull more amps to make up for the required wattage. If the battery is not producing enough amps the starter will attempt to pull more voltage.

The battery could be showing proper voltage, but not producing enough apps for the starter to work properly. Have you tried just jumping across the lugs on the starter relay? If doing so will spin the starter correctly to me it sounds like the battery is producing enough voltage and amperage to work the starter correctly. If not then I would have the battery tested. You can also use a car/truck battery to jump start (just do not have the car or truck running when you do so). Again if it turns the starter correctly then the issue is in your battery. If not then I would jump the starter directly to the battery and see if it spins correctly. If it does then it sounds like the relay to me.

I have tried going from the positive of my bike's battery directly to the relay and directly to the starter. Neither spun the starter. Haven't tried a car battery.

So to use a car battery to test it, I'd connect the negative pole of the car battery to the bike's frame and touch the positive pole to the starter post on the relay?

Is it possible for any malfunction of the starter clutch to cause this behavior or would I hear the starter whine if it was the starter clutch?

Hi Topper, do you have one of those portable car battery jumpers? Or better yet, pull the battery and take it to Advance Auto Parts or Autozone, they can do a cold cranking test on it. Might call ahead to make sure they can do it on a motorcycle type battery. I don't see why not.

Great minds think alike. I was heading out to run some errands so I took the battery with me and had it tested.

Battery is good. I'm getting 12v at the starter, so I guess there's nothing left but to tear into the left side of the bike and remove the starter.

Ok, it was definitely the starter.

I took the starter out and carried it over to my car. Hooked it up to the car battery with jumper cables at it spun, so I thought "must be the battery after all". But it seemed a little slow. And while spinning it would sort of speed up and slow down. So I tested it a couple more times. Sometimes it would spin, sometimes it wouldn't.

I took the starter apart and it was a mess inside. The commutator looked bad and there was muck all over the brushes. I cleaned everything with electrical contact cleaner and a soft brush. The muck was keeping one of the brushes from moving freely. I also sanded the commutator with some very fine sand paper and cleaned all the grooves in it out with a pick.

I put it all back together and hooked the starter up to my motorcycle battery with jumper cables. This time it spun so fast it almost jumped off the board it was sitting on.

One thing I still don't understand though. While I had the starter apart I tried a couple of the
tests listed in my manual.

First test says "Using the highest ohmmeter range, measure the resistance between the commutator and the shaft. If there is any reading at all the armature has a short and must be replaced."

Second test says "Using the Rx1 range, measure the resistance between any two commutator segments. If there is a high resistance or no reading between any two segments, a winding is open and the armature must be replaced."

I failed both of these tests (even after cleaning up the commutator). Nevermind that "high resistance" is kind of vague, I got no reading several times and I failed the first test with flying colors.

So given that my starter failed those tests, yet seems to be working... I thought I'd ask if anyone else has experienced this. Have any of you tested the commutator on your starter?

Was the same strip on the commutator also the one that failed the short to shaft test? If so you will have a bad armature. The starter, if two brush type, will not spin if/ when it gets Parked with one brush on the bad section of windings. It may also smoke, as there are no Fuses/ Fuse-links here on the starter circuit. Just straight battery power.
Another way to test is with a low wattage test light. You can supply power through the commutator sections to see if it light up the test light, good, and also if it lights up when hooked to the shaft, which it should Not, Bad.

Well, it pretty much failed the short to shaft test every place I tested it. Just to be sure I did it right, when the manual says "Using the highest ohmmeter range" I set my digital multimeter to 2000K (it goes from 2k-2000k). Is that the right setting?

I can't explain that for sure, as your doing the test. But did you have your fingers on the point of contact/ probe metal?
This is why I like the Old Test Light, it places a load on the circuit, puts juice through the windings. Old dude, does it the old way.