electric starter woes

[StoneGekko]

thanks to everyones help so far I can finally kick start my '78 gs750... some of the time...
other times it won't start to save my shins.. haha
took out the old starter and tested it... dead.. so i just put in a replacement.
the guy i bought it off tested it ( hooked it up to a car battery... spun like crazy) put it in my bike... and can't get it to spin...
I tried shorting across the contacts on the starter relay.. i tried a wire from the hot on the starter relay right to starter motor.. and nothing.. no noises (except for the clicking of the relay when i push the start button)

any ideas? should i be checking the grounding on anything ( i put a ground on the rectifier already and theres a decent one on the relay )

any help would be appreciated.. i'd like to get it starting on a regular basis

[Steve]

Use a test light to verify that you do have power coming to the starter.
If you have that, then make sure there is a good ground strap from the engine back to the chassis or battery.

.

[chef1366]

Make sure the starter gear and clutch are good.

[StoneGekko]

don't have a test light to check it.. but i used a voltmeter and it shows voltage (tho since its momentary it's hard to say how much...) i haven't checked the grounding to the engine yet... i'll do that tomorrow

as for the starter gear and clutch.. how do i check those? (i didn't take off the side covers when i replaced the starter motor... but i could feel the starter gear and it moved easy enough...

when i short directly from the hot on the starter relay to the starter motor, there's a small spark.. but the motor doesn't even sound like its turning

[SqDancerLynn1]

Do you have any jumper cables ? Connect to battery -- ground to engine / + cable touch it to the large terminal on the starter if the starter works great! that measn you need to work backwards to find your electrical problem. A wiring diagram will be a big help to you
Have you checked the battery ???