Author Topic: Ebay CB750 starting issues (Read 2291 times)

Msh5337 · « **on:** March 24, 2016, 12:49:37 PM »

So last week I let my emotions get the best of me and impulse bought a 1975 CB750 on Ebay. The guy said he rode it all last summer and all that was needed was a battery, and maybe a carb cleaning, to get back on the road. (I know, I'm an idiot for buying a non-running bike). It has 42k miles on it, but has supposedly had a top end done on it. After getting it back to my house and diving into it, I suspect it’s a little worse off than he was letting on. The goal right now is to get it running and see how bad of shape I’ve gotten myself into. I’ve already scoured through the forums and have found out the ritual to get it started. I’ve removed the tank, cleaned the petcock, replaced the fuel lines, and will clean the carbs tonight. I even have a new and charged battery. The only thing I’m stuck on is the wiring. It’s a freaking rat’s nest. I hooked up the battery and got nothing at all. No lights or anything. Took off the headlight and noticed the PO disconnected EVERYTHING! I’m not sure what connects where. My question is, what would be the bare minimum that I would need to wire up in order to get the bike to turn over?

flybox1 · « **Reply #1 on:** March 24, 2016, 02:39:39 PM »

wiring diagrams are plentiful...just google image search 1975 CB750 wiring diagram.

Download the PDF of the HONDA shop manual below...find the Periodic Maintenance section, and do all items listed for the 3000mi service
This usually fixes the majority of the issues.

http://www.honda4fun.com/materiale-documentazione-tecnica/shop-manual

Jerry Rxman Griffin aka MuthaF'er · « **Reply #2 on:** March 24, 2016, 02:55:41 PM »

Plug like color male bullets into female bullets.

2wheels · « **Reply #3 on:** March 24, 2016, 02:58:55 PM »

Did you take the ignition points cover off yet?
If it still has stock setup in there it is easy to hotwire it and then you can bypass all the wiring.
And hear the engine run, hopfully.

Msh5337 · « **Reply #4 on:** March 24, 2016, 04:14:02 PM »

Thanks for the fast relpies guys. I'm planning on ordering a new wiring harness and redoing everything anyway. I just wanted to know how to quickly get it started just for the time being. Yeah Jerry, I'm a goon when it comes to electrical stuff, but that much I do know. Lol.

No, 2wheels, I haven't tried that yet but it sounds like a good idea. Will it try to turn over then and there, or will I still have to kick start it?

Stev-o · « **Reply #5 on:** March 24, 2016, 04:32:29 PM »

Your not an idiot for buying a non-running bike, most bikes I buy dont run when I get em.

Just dont ever believe what a seller says! Sure, it ran when parked then he let it sit for a year. The carbs will need to be cleaned and motor given a full tune after you get the wiring reconnected.

Do you have a lot of cut wires? If no, you may not need a new harness.

Relax and take it one step at a time.

Hope you didnt overpay! Last non-runner I bought was $700.

2wheels · « **Reply #6 on:** March 24, 2016, 05:41:39 PM »

Hot wiring, or really just bypass the key and kill switch, will only allow spark.
You will still have to kick it over.

ekpent · « **Reply #7 on:** March 24, 2016, 08:00:51 PM »

Post up a pic when you get the number of posts or figure out photo bucket, they are worth a thousand words., Lets see if its a stocker or a Frankenstein. When ever I hear the words top end done or other things I get nervous when thinking about a bike because I would not maybe trust the seller or mechanic--- UNLESS he was an esteemed member here, and even then it still may have a leak

I like to be the first one to F it up

mystic_1 · « **Reply #8 on:** March 24, 2016, 08:13:40 PM »

"Rode it all last summer, all it should need is a battery, and maybe a carb cleaning, to get back on the road"

mystic_1

mystic_1 · « **Reply #9 on:** March 24, 2016, 08:14:39 PM »

Oh and here's a wiring diagram for you.

Stev-o · « **Reply #10 on:** March 24, 2016, 08:50:30 PM »

Quote from: mystic_1 on March 24, 2016, 08:13:40 PM

"Rode it all last summer, all it should need is a battery, and maybe a carb cleaning, to get back on the road"

mystic_1

That outta buff right out!

Msh5337 · « **Reply #11 on:** March 25, 2016, 11:01:01 PM »

SHE'S ALIVE!!!!!! It was a nightmare wiring everything back up, but I got it finished. And the wiring harness isn't as bad as I thought. Nothing was cut up, just mainly had things plugged into the wrong spot. Not exactly sure what the PO was doing. Anyway, she's running! Thanks for the help and the pep talk. For future reference to anyone who sees this post, this is the best wiring diagram I was able to find for a 1975:

http://picasaweb.google.com/lh/sredir?uname=the.xenos&target=PHOTO&id=5432602827904232594&aid=5432602713157926337&authkey=Gv1sRgCMX6s__npKLooQE&invite=CIujrKEN&feat=email

Someone on this forum named XenosCR made it.

Msh5337 · « **Reply #12 on:** March 25, 2016, 11:08:15 PM »

Oh, and one more dumb question. How noisy are these engines supposed to be? It doesn't sound like there is anything wrong with it necessarily, it's just quite a bit louder than what I'm used to. And I'm also getting some popping from the exhaust while the engine is warming up. Any idea what that might be from?

Stev-o · « **Reply #13 on:** March 26, 2016, 04:53:59 AM »

These motors can be noisy, especially when at low idle. A vacuum sync of the carbs typically reduces it.

mystic_1 · « **Reply #14 on:** March 26, 2016, 05:43:16 AM »

Yup, if it gets quieter when you pull in the clutch, that's pretty common.

mystic_1

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