Topic: Why does my starter slow down?

[DammitDan]

 1982 CB650 std with an '82SC engine.

I've noticed (more like feared) a peculiar phenomenon when my bike gets nice and warm after a long-ish ride. If I stop somewhere for a few minutes and cut the engine (like at a gas station), when I try to start it again the starter acts like it's "tired" and just Whirrr.. whirrrrr...... whirrrrrr's like the battery is dying. However, if I hit the starter with the throttle slightly open it will turn over instantaneously. I don't think it's the battery going cause it runs plenty strong after it turns over and I keep her charged and maintained correctly. And if I let the bike cool down for an hour or so the starter will spin the engine and turn it over effortlessly.

I've got an extra starter at home, and I know they can go bad, but why does mine only go bad when the engine is hot? I initially thought the damn thing was getting hot enough to slightly sieze (making the starter have to work very very hard), but then I found that I could turn the engine while in gear by hand with the rear tire.

What could my problem be? And why the hell didn't they give 650s kickstarters?!

[ProTeal55]

Dint fret Dan , my CB750 does the same thing.

When cold, the starter cranks over like in a car, fast and responsive.
After the bike is warm , it cranks over real slow, and seems like their is a battery issue.
I am guessing it is a heat-soak issue, like most older muscle cars have with "hot starts"

Maybe I am wrong , but I dint believe it to be an issue.
It has done it from the day I got the bike, and prob. will for as long as I have it.
As long as it works - I am fine with it...

[TwoTired]

It's time to crack the starter open and inspect the brushes and the bearings.

Cheers,

[Tim.]

Mine does the same when hot.  Can't even turn the engine over, but will fire right up with the kick starter.  Frustrating if I stall for some reason, but I manage.

[StevieMac]

Don't know if this will help or not but for what it's worth....

I do know that older Yamaha Ventures (totally different bike I know....) have the same issues I.e starts fine cold but starter turns over too slow once the bike is warm.   Many owners have found that replacing/upgrading the cables from the battery to the selenoid/starter & the battery ground wire to a heavier gauge wire solved the problem completely.  4 gauge wire is the solution of choice on the Venture forum.

[Andoo]

It may be because when the engine is hot the compression is higher due to expanded piston rings, ect. With a tighter seal the higher compression is harder for the starter to crank over.  im sure somebody will show im wrong

My CB750 does the same.

[ProTeal55]

Many owners have found that replacing/upgrading the cables from the battery to the solenoid/starter & the battery ground wire to a heavier gauge wire solved the problem completely. 4 gauge wire is the solution of choice on the Venture forum.

Makes sense.
As the racecar guys do the same thing, but they usually use zero gauge wire.
4 gauge would be more than enough on a bike..

Good tip....

[Bob Wessner]

Interesting thought on the wire gauge, but I think there is something else going on. A hot engine and higher compression wouldn't seem to matter a much as oil viscosity, much lower when hot. Mine turns and starts much easier when hot than cold. Consider a cold start in March vs. a cold start in July. The starter works harder in March.

[TwoTired]

A bit off topic, I guess.  But, I just had to replace the brushes in the cb700SC starter. 
Symptom:
spins fine and a good long while when cold.  After warm up, turned very slowly, frequently wouldn't spin fast enough to start the bike.

This starter has 4 brushes in it.  One brush was gone (worn out and laying in the bottom of the starter).  The other brush for the same pole was nearly gone and the wire leading to it was melted through and making intermittant contact.
New brushes, dressed the commutator, problem solved.

Cheers,