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Electrical issue

jdibiase

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Hey all! This is my first thread I am starting. I would like to say thank you for being such an amazing resource! I just purchased a 1981 honda cb750c. It is fully dressed as of right now and might have a lot of parts for sale in the near future. I would like to get it running first.

Ok here is the issue.

When I went to pick it up on Tuesday, the guy I got it from gave me a huge box of extra parts, with a starter in it. He hooked it up to the battery that he bought last year at fleet farm. Nothing. He went in the garage and got another battery that was charged and all the lights worked and it cranked. I heard it crank. He gave me the battery that he got last year (the one didn't work while I was there) and I drove the whole bike home. I threw the battery on a charger and left it for a day and a half.

When I tried it I had full lights and everything but it just "clicks" by the positive lead of the battery terminal when I hit the starter button. I think the battery is SHOT so I returned it at fleet farm and they gave me a brand new battery in exchange for free (it wasn't 12 months since he bought it last). I haven't hooked it up yet BUT i did try to jump it with my lawn mower (brand new last year and it was running). The lawn mower was running and I had full lights and electrical on the bike. I tried to crank and got the same clicking noise by the positive lead on the motorcycle. I check the main fuse and changed it (it wasn't out either). Still nothing except that click on the positive side of the motorcycle.

Where do I go from here? I think I saw the ignition fuse box by the handle bars and I haven't checked it yet. Other than that, should I try the other starter in the box (I will test it before I install to save headache)? Is there something that I am missing? This is my first 4 cylinder and am pretty excited. What I don't get is I heard it CRANK at the guys house. It didn't crank long, but it definitely cranked.

Any help would be super appreciated! Thanks in advanced!

-Joe
 
You say you hear clicking by the positive battery terminal... maybe I'm nit-picking, but for clarification please confirm whether it's one click you hear, or multiple clicks.

My assumption is that it's probably multiple clicks and it's coming from the starter solenoid. One end of the positive cable connects to the battery + terminal and the other end of that cable connects to a terminal on the starter solenoid. Connected on the starter solenoid right next to the positive cable from the battery is another cable that connects to the starter. Look at this wiring diagram at the upper RH corner where it shows the starter relay (this is what I refer to as the solenoid).

http://www.cb750c.com/publicdocs/CB750K_wir_diag/Wiring_Diagram_CB750C_81_82.pdf

When you press the start button this relay should shift and connect the two relay terminals... this connects battery positive to the starter. The starter is grounded so you now have + and _ to the starter motor and the starter should be cranking.

Sooo... if you hear just one click, it could be that the solenoid has closed, thus the one click, and the starter should be working unless there's a bad connection, bad starter, or bad battery. You think the starter is good and the battery is good and charged, so check to be sure connections are tight at the battery, starter solenoid, and starter. Be sure the negative battery cable is tight both at the battery and at the other end of the cable as well.

Now... if we're taking multiple clicks coming from the solenoid, could be some of the same issues such as bad connections or bad battery... there's maybe not enough power to keep the solenoid closed so the starter will crank... or maybe the solenoid is just bad. If it was me, I'd just touch a screwdriver between the two large terminals on the starter solenoid to close that circuit just like the shifting solenoid would do. If it cranks, the solenoid is probably bad. If it still doesn't crank, could be those bad connections, bad battery, or bad starter.

If you decide to use the screwdriver test, be aware that there could be some sparks on the screwdriver... don't use one that you don't to get a black spot on or maybe burn the end. The sparking could also burn the terminals threads a little (or a lot). The key would be to touch both terminals like you mean it... don't sneak up on it, make a good connection. If it cranks right off, everything will be fine. If it doesn't crank right away, don't leave the screwdriver in there... if smoke comes out, that won't be a good thing. We always want the smoke to stay in the solenoid, wires, switches, etc.... if it gets out, something isn't right.

Disclaimer!!! What I described is no big deal, but there could be some risk of sparks, release of smoke, pits in screwdrivers, and for the meek, a wet spot on your britches.

Report back on your actions and results, please.
 
You say you hear clicking by the positive battery terminal... maybe I'm nit-picking, but for clarification please confirm whether it's one click you hear, or multiple clicks.

My assumption is that it's probably multiple clicks and it's coming from the starter solenoid. One end of the positive cable connects to the battery + terminal and the other end of that cable connects to a terminal on the starter solenoid. Connected on the starter solenoid right next to the positive cable from the battery is another cable that connects to the starter. Look at this wiring diagram at the upper RH corner where it shows the starter relay (this is what I refer to as the solenoid).

http://www.cb750c.com/publicdocs/CB750K_wir_diag/Wiring_Diagram_CB750C_81_82.pdf

When you press the start button this relay should shift and connect the two relay terminals... this connects battery positive to the starter. The starter is grounded so you now have + and _ to the starter motor and the starter should be cranking.

Sooo... if you hear just one click, it could be that the solenoid has closed, thus the one click, and the starter should be working unless there's a bad connection, bad starter, or bad battery. You think the starter is good and the battery is good and charged, so check to be sure connections are tight at the battery, starter solenoid, and starter. Be sure the negative battery cable is tight both at the battery and at the other end of the cable as well.

Now... if we're taking multiple clicks coming from the solenoid, could be some of the same issues such as bad connections or bad battery... there's maybe not enough power to keep the solenoid closed so the starter will crank... or maybe the solenoid is just bad. If it was me, I'd just touch a screwdriver between the two large terminals on the starter solenoid to close that circuit just like the shifting solenoid would do. If it cranks, the solenoid is probably bad. If it still doesn't crank, could be those bad connections, bad battery, or bad starter.

If you decide to use the screwdriver test, be aware that there could be some sparks on the screwdriver... don't use one that you don't to get a black spot on or maybe burn the end. The sparking could also burn the terminals threads a little (or a lot). The key would be to touch both terminals like you mean it... don't sneak up on it, make a good connection. If it cranks right off, everything will be fine. If it doesn't crank right away, don't leave the screwdriver in there... if smoke comes out, that won't be a good thing. We always want the smoke to stay in the solenoid, wires, switches, etc.... if it gets out, something isn't right.

Disclaimer!!! What I described is no big deal, but there could be some risk of sparks, release of smoke, pits in screwdrivers, and for the meek, a wet spot on your britches.

Report back on your actions and results, please.

Not being Nit-picky at all!!! It is definitely ONE click. Just one. When I get off work, I will try to make sure there are no loose wires (I can't believe I didn't do that already....KISS principal..ush). I will update as soon as I get home! Thank you for the response!

Joe
 
Scary as it might sound, and would for sure if you knew me... I just had a thought. Maybe total nonsense since I've never been into the wiring of a 750C, so keep that in mind.

I did, however, have a CB900C, and if I recall correctly, the engine was mounted with rubber isolators. So what comes to mind is that there needs to be a good ground from the frame to the engine for the starter to work. Again, if I remember correctly, on my 900 there was a ground cable on the RH side of the bike just to the inside and rear of where the driver footrest was. It may have been a separate cable, or may have been an extension of the cable from the - battery terminal... sorry, it's been awhile and I've slept since then.

In case I'm right, be sure there's a good ground between the frame and engine. Your bike may not have rubber isolators and this may be totally wrong, but again... I had a thought.
 
Well. I looked at the manual section for engine removal and see nothing that looks like rubber isolators, so that doesn't look to be an issue. You might look at your mounts to be sure, but my thought was just that... and scary.
 
tommycarl,

I checked the mounts and they are hard mounted. No rubber insulators. I tried to replug in the connectors and still the same problem occurs. Just one click. The rubber insulator on the solenoid looks like it overheated and is melted. I don't know how to post pictures yet but I did take two. I think I'm going to replace the starter solenoid. I think it might be the issue. Can I purchase an "after market" on flea-bay or should I spend the extra $ and get Honda original? The price difference is quite a lot.

Thanks!

-Joe
 
I've never had an issue with aftermarket solenoids. You apparently didn't try a screwdriver... you'll know in an instant if the solenoid is the issue.
 
I will try that right now. So I hook up the battery then take a screwdriver and put them on the positive and negative leads (where the MAIN FUSE is located and hooked up to). If it cranks, the the solenoid is good. If I see smoke... then bad. Right?
 
Here's a solenoid that I think should look like yours.... the two terminals with nuts are the ones to connect. Yours should have cables on them. (you're not going to see any smoke) Turn the key on if you want the bike to start.... it'll crank even if it's off.

http://www.ebay.com/itm/Fast-Ship-S...fits=Model:CB750C&hash=item339ab170f2&vxp=mtr

Boom! It cranked. You weren't kidding about the sparks! July Fourth 101. I jumped the first time and I was wearing gloves (because safety is not a laughing matter). Does that mean the solenoid is bad since it cranked?

Thanks tommycarl!

-Joe
 
Sounds like the best guess to me. All the solenoid does is complete the same circuit that your screwdriver did. I AM making the assumption that the click is solenoid shifting and could be wrong, although I don't know where.

You tried to be sneaky, didn't you!!?? I warned you! lol

I suppose it's going to cost you $10 and a few days to find out for sure... I'd get the one NOT from China since it'll take longer to get it. lol

Now the important question... did it start?
 
Sounds like the best guess to me. All the solenoid does is complete the same circuit that your screwdriver did. I AM making the assumption that the click is solenoid shifting and could be wrong, although I don't know where.

You tried to be sneaky, didn't you!!?? I warned you! lol

I suppose it's going to cost you $10 and a few days to find out for sure... I'd get the one NOT from China since it'll take longer to get it. lol

Now the important question... did it start?

Yea I was sneaky.....Couldn't be sneaky about it. I just tried it with the key on the off position. The fuel tank is taken off of it. The tank needs to be emptied with the gas that's in it and then cleaned with CLR. The carbs will also need to be removed and thoroughly cleaned it sat for the last 3 years indoors. I don't want to run bad gas through it and get all my bases covered.

I am very apprehensive about cleaning the carbs and getting them synced. I use to ONLY work on 2 cylinders (cx500 models). This is my first 4 cylinder and the carbs are way more complicated. I bought an ultrasonic cleaner today. I want to get on the road as fast as possible but I need to make sure the bike is in better shape maintenance and safety wise (for seals, rear tire, cam chain brake checks, etc)

Any tips on carb cleaning? I downloaded the 42 page guide on a thorough cleaning but that might take a few weeks with my schedule. You know anyone that would clean them (within a reasonable price)?

Thanks for all your help! Big jump on the progress!

-Joe
 
I assume this is the 42 page manual you mention: http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf

I recommend the screws and o-rings on page 42. I've bought more than 1 set myself.

On the other hand.... I'd be trying it just the way it is, with fresh gas, of course. But then, I'm pretty impatient and wanna know if the darn thing will run! take the gas tank off your lawn mower and hang it from the ceiling... just make sure the hose reaches the carbs (and keep those sparks away from the gas!!) lol

Depending on how dirty the carbs look after you get the bowls off, I'd even consider just spraying them well with carb cleaner (some think that brake cleaner is better, but I prefer carb cleaner). If they seem too dirty for that, and if you really don't want to take them apart, soak them in Pine-Sol for a day or so... not much work in that, and Pine-Sol works pretty darn well. Get a guitar E string for the small holes in the jets, that works well too.

The manual makes it sound complicated and difficult, but I'd say you could get the disassembly / reassembly done in 3-4 hours even if you study the manual as you go. If you're going to bypass the air cutoffs, I found that a slice from the old oil filter o-ring worked for me... the right diameter, and a small slice was easy to get.

There are a couple of fellas I could send you to for cleaning, but I'm not for sure that they do DOHC carbs. If I remember correctly, the cost is in the $300 area... but you really want to learn how to do this yourself... use the money to buy the right tools for the synch screws and a good tools for synchronization. Trust me, it isn't hard if you have any patience and desire... 90% desire, 9% patience, 1% skill, (I made that up).
 
I just messaged a fella who is supposed to be good at cleaning carbs for SOHC bikes... maybe he does DOHC too. If he's interested in cleaning yours. he should send me his email address.

Maybe someone here will chime in with a suggestion.
 
By the way Joe, I need to apologize for making the assumption that this was your first bike and maybe sounding like you didn't know much about them... and kinda went overboard on how a starter solenoid works. I honestly was just trying to be sure I didn't lead you in the wrong direction and have you somehow not understand what I was trying to explain. I've sometimes found that even terminology can be an obstacle, and try to be as clear as I can to keep things as safe as possible, yet effective in getting to the source of an issue.
 
By the way Joe, I need to apologize for making the assumption that this was your first bike and maybe sounding like you didn't know much about them... and kinda went overboard on how a starter solenoid works. I honestly was just trying to be sure I didn't lead you in the wrong direction and have you somehow not understand what I was trying to explain. I've sometimes found that even terminology can be an obstacle, and try to be as clear as I can to keep things as safe as possible, yet effective in getting to the source of an issue.


No need to apologize. When I worked on those other bikes, I lucked out on all of them that the electrical was in tip top shape (total of 5 bikes). Electronics is pretty much a second language. I did not know how to short out a solenoid and I really appreciate the help! I can do mechanics fairly well. I just need to learn how to take apart 4 carbs with confidence. I know I can do it, but I have a lot on my plate (redoing my house and landscaping, grad school while working full time). I'm just like you, I REALLY want to ride since the weather is warming up here in wisconsin but i cant invest the time into this bike right now. Let me know if he responds! If not, I think I will buy the software and hardware on page 42 of that pdf and go from there. I like that pine-sol idea too.

Thanks again tommycarl. It has been a great welcoming to the forum and you helped a lot!!!

-Joe
 
You're too kind Joe.

I probably shouldn't tell you, but I've posted it enough times already that the word is out.... I say that cleaning the carbs is easy, but it actually took me 6 times to get the job done on my CB900C. Uncharacteristic of me, at least I didn't keep telling myself it COULDN'T be the carbs because I just cleaned them (1...2...3...4...5 times) before I got to 6.

The nice things about the Pine-Sol include that it does seem to work, makes the place smell nice, can be used more than once, and makes the carbs look pretty nice all over. I know... my opinion doesn't mean so much now that you know it took me 6 times. lol
 
Yargity. I have a dohc 79 cb750 and was so incredibly apprehensive about messing with the carbs (twas my first bike experience). I did a complete and total breakdown, down to the last spring and screw. Replaced every bit of rubber, but the accel pump (I'm a dummy). Took me about a week including soak times. I also spent around $180 on new jets and brass pieces and rubber, and air cutoff valves. You can do it for much cheaper (or free if rubber is good). They were a PITA, but I felt awesome once I pieced them back together. My advice is as follows:
1. Take some F***ing pictures, it can save your butt.
2. Record the number of turns of any gas/fuel screws so that you can put it back together the same and adjust from there.
3. Only break the four carbs off the rack if you really want to. I'm glad I did, but lining all of it back up had me so mad I almost gave up. It also turned a 4 hour job into a 7 day job.
4. Use elbow grease. You'll want a tooth brush or two, some guitar string or carb tool. There's no point in opening them up just to half ass the job (IMO). There's all sorts of hidden crap to scrub at.
5. Be patient, and understand and research the function of each and every part of the carb, because not all are the same. This is arguably the most important piece of your bikes performance, its the heart/lungs.

These guys aren't lying. Of all the things I've done since, learning how MY carbs work, has been the most "rewarding" experience as far as maintenance type task. If you have questions about any of the pieces just ask. I'm sure my kehins are just about the same as yours.
 
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