Topic: Sluggish Starter Motor

[Jbholts]

I finally rescued my CB750 K1 from the garage where it sat for 5 years under boxes of Christmas lights, old rugs, etc. It is nearly back up and running but one issue has me stumped. First, I did have this issue when I parked it 5 years ago. The bike will start with the kickstarter no problem. When I use the starter though, it sounds like it is not getting enough power. It turns the engine but in jerky increments and with a high pitched squeal. It may start that way 1 out of every 10 tries. The bike has a 836 Wiseco kit but is otherwise stock. The battery is new and fully charged and I cleaned every connector. I tried jumping the starter solenoid but it didn't change anything. Thanks for any suggestions.

[DaveBarbier]

Sounds like the starter is toast, no? They may be rebuildable but I doubt a good used one off eBay is expensive.

Have a spare off another bike you can test? Squeal is coming from the starter? If you remove the starter and bench test it it still squeals?


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[Bodi]

The starter is rather simple, a series wound motor. Check the brushes by unscrewing the caps and pulling them out. They should go back in the same hole, same orientation. You want a springy spring as overheating will make them unspringy. Amd a decently long carbon piece, I don't have a measurement but service limit should be in the service manual. Look down a brush hole with a light. The commutator will be dirty but the copper sections should be distinct, not smeared across the insulation sections or badfly burned and scored. You can dismantle the motor for full inspection, cleaning, and commutator dressing but these motors are rarely found worn to need it... they don't get that much running time in normal use.
But... your problem sounds like a slipping sprag clutch. That is on the back of the alternator rotor. It has a heavy steel ring with 3 pockets for the 3 springs, 3 spring caps, and 3 decent sized rollers. Lots goes wrong with these, you should inspect it. The ring must be solid (they crack), all other parts must be present and in good condition (somehow springs and caps manage to escape) . The starter gear extended part is the driving centre of the clutch and it's outer surface should be smooth.

[Jbholts]

Thanks guys for the details! I think I will go ahead pull the starter and inspect/bench test it. I hope that's it. Reading some other posts about bad starter clutches, it does seem like that may be my issue. If that is the case, as much fun as pulling the rotor sounds, I think I may just kickstart it until winter.

[Jerry Rxman Griffin aka MuthaF'er]

Pulling the rotor is easy, easier than pulling the starter motor, IF you have the right inexpensive tool. An air impact wrench helps too. Takes a couple seconds in that case. Also take a look at the flange on the gear the rollers hit for out of roundness. If your starter clutch is getting worn out it may not engage or it will disengage and spin freely without moving the crankshaft.

Also you may consider the clutch is dragging after sitting that long.