Topic: scarey noise

[mrblasty]

twice today my bike made a weird noise.
Kind of loud whirring/whizzing noise louder than the cam chain noise.
The first time it happened Immediately after take off at a traffic light, the second time I was waiting at traffic light and the noise just came on.
Also when turned the key on my starter kicked and I about lost the bike.
Today was the first time in a week it had been ridden and all of this happened after about two hours of ridding.
The bike is a 750 k3.  Any Ideas?

[Dennis]

Is your starter motor running when it shouldn't be?
That's what your comment about turning on the key leads me to think.
There could be a number of malfunctions causing this, like shorts or a damaged switch. If this is what is occurring, the first component I would look at would be the solenoid. Relays (which is what it really is - a high capacity relay) can hang up when they get old and worn or if they have been abused.

[TwoTired]

Hows your starter button feel?

[dpen]

Starter buttons get full of crud & stick.

Separate the handlabar switch & hit the insides with some WD40 (if you're not mechanically minded), if you are, the switch is easy to pull apart & clean up (watch out for little springs that like flying out.)

[dusterdude]

sounds like the starter to me too

[TwoTired]

Starter buttons get full of crud & stick.

Separate the handlabar switch & hit the insides with some WD40 (if you're not mechanically minded), if you are, the switch is easy to pull apart & clean up (watch out for little springs that like flying out.)

Please don't use WD40 on the switch plastic parts.  The solvents attack the plastic and leech out the plasticizers.  The plastic gets brittle, cracks, and falls apart.

There are lots of spray cleaners/lubes that are plastic safe and clean well.  They will say so on the labels.

Cheers,

[Jonesy]

CRC makes a spray cleaner for electrical connections that's safe for plastics. You could give that a try...

[mrblasty]

I haven't had a chance to look at it, I suspect a loose connection in the head light bucket, before the occurrence my headlight flickered..hmmm

[TwoTired]

I haven't had a chance to look at it, I suspect a loose connection in the head light bucket, before the occurrence my headlight flickered..hmmm

Then it is almost certainly your starter button.  When you press the stater button, it interupts the headlight circuit.

Basicly the button has three contacts; center 12V, headlight (Normally on), and starter solenoid activate (momentary on).
 If the little rocker and contact are floating around inside the switch housing, vibration will give you random starter activation and headlight outages.

Did brake fluid from the master seep into the control housing?  That will ruin the plastic internals and the electrical bits will wander wherever.

Cheers,

[dusterdude]

see blasty,the old timer,i mean two timer,damnit i mean two tired hooked you right up.

[Dennis]

I haven't had a chance to look at it, I suspect a loose connection in the head light bucket, before the occurrence my headlight flickered..hmmm

Then it is almost certainly your starter button.  When you press the stater button, it interupts the headlight circuit.

Basicly the button has three contacts; center 12V, headlight (Normally on), and starter solenoid activate (momentary on).

Did they have that style starter button on the K3's?   
I know my 750F has it but that's a couple of years later. I don't know when they started that. My '73 Yamaha and my '75 Elsinore Enduro both have headlight switches. My '84 Yammie has no switch, headlight on at all times.

[TwoTired]

I rechecked the schematics.  Looks like the Cb750K didn't get the starter button headlight interupter 'til 76.

Seem odd, that.  My old 74 CB550 has the interupter.

Sorry, I just assumed the Cb750 was more advanced than the Cb550. 
Guess not.