Slow starter motor

[tj2]

Hi all, have done a search but nothing specific as a reply to my problem.

I have a 75 GT750 which is currently being restored/rebuilt. The starter motor appears to be very slow on standard battery and not much better on a car battery. When the starter is run off the bike appears to be normal.
When run on bike (no cylinder head) spins the engine fast. Head back on (no plugs) spins engine relatively fast.
With plugs back in barely turns over.

The earth from engine to frame is a braided flat cable with good contacts, the solenoid is new.

Any ideas of where to go next?

Cheers Terry

[Alan H]

The motors get 'tired' and usually need a refurb.
If the battery is good and all connections from battery to motor and battery to earth are good then it'll need servicing.
Motobatt batteries are better than lead acid regarding 'umph' for starting. I have them on my kettle and 550s.
Contact Barry - he refurbs them. I've pm'd you his email details.

[akendall1966]

Hello,

Any given DC electric motor speed of rotation is related to the voltage applied and torque it develops to the current. Under little load (not much torque needed) yours appears to spin up OK, when under load it struggles. As you have tried different batteries and get the same result it not likely to be the batteries ability to deliver high enough current, so something else is stopping the wingdings getting the full current available.

Have you tried jump leads from a car battery directly to the motor terminals with spark plugs in? If its still not developing enough torque to spin the motor over fast enough your problem is in the motor. If a direct connection to the motor is OK, its somewhere in the external circuit. The solenoid might be new, but might not be good. Jump lead to the solenoid output will verify the wiring to the motor, the motor and on to ground. Obviously be careful what your touch with the jump leads as the potential for damage / fire from an accidental touch/spark exists.

If it is in the motor you have got a high resistance path somewhere and its time for a refurbish as Alan suggests. Brushes , commutator, internal connections all could be loose, corroded, dirty or just worn out.

AK

[tj2]

I have run the leads direct to the motor from the bike battery and car battery ...same effect.

The starter looks as new but has been stood for a while.

Looks like a strip and rebuild of that then.

Here comes the money pit

[akendall1966]

You might be lucky dirty / stuck brushes or bit of fine wet and dry on the commutator to clean it up.

Fingers crossed for you.
AK

[tj2]

I bit the bullet and stripped the starter.

Does anyone have the spec for the screws??? Had to cut them off.

Full of carbon debris, black commutator etc both bushes/ bearings good and surprisingly still a fair amount of material left on the brushes.

So Hopefully a good clean new brushes and new screws and it will be as good as new again.

[tj2]

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Well that didn't work.

Any ideas?

Terry

[akendall1966]

Open circuit winding(s)? Check the resistance between opposite commutator segments should be about the same.

Assuming its a permanent magnet motor, could be weak magnets.

[Alan H]

^^^^^^^^^^^^^^^^^^^^^^^^


Well that didn't work.

Any ideas?

Terry

Check your pm's.

[tj2]

Fixed, replacement starter obtained suction test done seems that crank seals are good!!!!!