Starter cranking slowly

[PugNug]

1983 GS850g

About three months ago, I went to start my bike and I hit the starter and I just heard a click and this groaning whirring noise, I could hear the Bike turning over, but it sounded like it wasn’t getting enough power. The only problem is it doesn’t seem like my battery is running out of juice because once I bump start the bike and even before I bump start it all of the electrical is working perfectly fine. Headlight turns on turn signals work and it doesn’t have a problem cranking if I jumpstart it
I also tested my starter solenoid and it clicks and seems like it’s activating just fine.
I took my starter out and bench tested it with a known good truck battery and it seemed to spin just fine. It spun with no problem
is there anything else I should test before I just start replacing things all my fuses are fine and the battery has never given me trouble before
If anyone could help me I’d really appreciate it. I’d love to keep riding without having to bumpstart this thing every time.
thanks a bunch

[1978GS750E]

Take your battery to an auto parts store and have them test it.

The starter draws the most battery current of anything on the bike. It likely has enough power to run the lights, etc. but not the starter!

I'm betting your battery is on the way out, since it starts fine when you jump it!

[Rich82GS750TZ]

…. sounded like it wasn’t getting enough power…… doesn’t seem like my battery is running out of juice…….. it doesn’t have a problem cranking if I jumpstart ….. a known good truck battery …. and the battery has never given me trouble

When one uses phrases like these but does not list any numbers, it could lead us to believe that you maybe have not measured battery voltage at all.
If you could get a voltmeter on your battery terminals and give us the DC volts with
Key off
key on
while pressing the start button

and yes, a load test at autozone or others as suggested by Ron could tell you a lot.

[PugNug]

OK, so I went and Borrowed a multimeter
with the bike completely off I’m sitting around 12V to 12.2 V
when I just turned the key on it drops to about 11.7 V
And when I actually crank the bike, it drops to about 9.5 V and stays there while I’m cranking
The second that I stopped cranking it and I turned the key off the voltage jumps back up to 12.2V
does that mean my battery is bad? Just let me know thanks

[Rich82GS750TZ]

Pretty much. Auto parts stores will load test your battery for free.
but your resting voltage is also low. You should begin testing with your battery full charged. Somewhere in the neighborhood of 12.7
Buy your own voltmeter. You own a 43 year old motorcycle. You need one.

[rphillips]

I agree, batt. seems low. Good shade tree test, While watching how bright the headlight is try to start the bike, if headlight dims drastically, batt. is low, if batt. is good you'll barely see it get dimmer... As always, just my opinion.

[chuck hahn]

Hook jumpers to car battery ..car not running. If the symptom clears it says the bike battery isnt creating proper cranking amps. Stays the same says starter motor is going away.
Had same symptom on y KZ750 for a few years in spite of several batteries. Then one day it started smoking when cranking. Dont wait till it gets to this point.

KZ STARTER.jpg

[adam83]

You may be experiencing what just happened to me. My battery test fine, electrical connections were solid, the case-to-battery ground cable was in great shape, and the positive leads from battery-to-starter were all in good shape too. So I removed the starter and looked inside, it was very dirty. I cleaned it and got a caltric rebuild kit. Pretty easy job if you are careful and mark positions of everything before taking apart. Long story short the starter was my problem and the fix was cheap.

Besides the general gunk that was inside, the main problem is where the brushes contact the commutator. The surface that the brushes ride on get corroded and dirty, and creates resistance. Here's a before and after of mine after cleaning.