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79 CB750 Starter issue?

MrMojoRisin

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Hello, just brought home a 79 CB750L project. Bike is partially together and was able to get it running with some jumper cables and starter fluid at the previous owners place before making the purchase. Once i got it home, i tried again as i wanted to do a compression test. Yeah, i know, should have done that before i made the purchase, but got so excited when it fired up that I... well you know.

Anyway, when I try to fire it up, I get the loud solenoid click and nothing else. If i try jumping the solenoid, sometimes I can get the starter to turn, but it turns slow. I decided to pull the starter and when I direct wire it, it spins, but every other starter I've done this with almost jumps off the table when power is applied. This starter spins up, but not with the torque i'm used to seeing. Battery is new, so i'm pretty sure that's not the issue. If these starters don't need the torque due to starter reduction gear or clutch, could i have a bad ground that is causing the issue.

Any help would be appreciated.

Thanks,
 
Ok, took starter apart and was surprised how clean it was inside. Obviously had been rebuilt at some point. Still cleaned up the contacts and checked the brushes out it all back together. Hooked it back up to the battery and put my voltmeter on it to test. 12.48 volts at connection ends and dropped to 10.6-10.9 when spinning. Little more drop than I was expecting but still should turn over.

Reinstalled starter in bike, hooked up and tested voltage at solenoids battery post @ 12.48. But voltage at starter post when hitting start button was only 9.34 volts, also noticed some smoke at the jumpers ground connection. Bike would alternate between solenoid click and slowly turning starter. Starting to suspect my issue is a grounding issue... any feedback would be appreciated.

Thanks,
 
Check and clean the ground connections ensuring good metal to metal contact. May need to charge the battery as it has likely drained with the testing. 9v under load is too low.


 
If the battery jumper cables are too small like so many now it will not jump, you got volt but no amp due to crap cables.
 
Check and clean the ground connections ensuring good metal to metal contact. May need to charge the battery as it has likely drained with the testing. 9v under load is too low.

Thank you... after doing a bit more looking over the bike, I realized that the previous owner only had two of the long motor mount bolts installed, and one of those was just a long pc of 3/8" all thread with two stainless acorn nuts. The upper rear motor mount bolt is supposed to have the ground ring for the battery gourd cable (i believe) and it's MIA. I'm going to reinstall those long bolts and will clean up the areas where the bolt/washer/ground wire ring contact the frame.
 
If the battery jumper cables are too small like so many now it will not jump, you got volt but no amp due to crap cables.

Thanks amc49...

Realizing that it's time for a new set of jumper cables. There is no question that these are undersized for anything useful. Never realized it until i pulled them apart after reading your post. Actually embarrassed that I've been using these pcs of junk for this long without realizing it.

appreciate the help.
 
Ok, well new jumper cables did the trick. Thanks amc49. Turns over just like it should. Now wondering if I need to replace my crappy old compression tester. Here were my results, cold & wot..

Compression test
Cyl #1- 122
Cyl #2- 66
Cyl#3 - 81
Cyl#4- 92

Surprised that it would fire on starter fluid with results that low. To make sure I didn’t imagine it, I put the plugs back it, sprayed in a touch of starter fluid and it fired right up. Here’s a link to a YouTube upload.

https://youtu.be/X6m_6KP7AXw

It’s been so long since I’ve owned an inline 4 that I’m not sure if that sounds right or not.

I’m gonna try again tomorrow, thinking I’ll try to hook up a temp fuel source to limit how much starter fluid I throw at it. Then I can see if it will run long enough to hear it better and see how it sounds.
 
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