Needing help with regulator and rectifier for cb750 Honda

[cruzin]

I am helping a friend of my son rewire his 78 cb750k8 bike. Going to rip the old harness out and do a simple wiring job with new blade fuse box or in line holders. new vr-115 regulator and a 50 amp 3 phase rectifier. This is a points bike with separate regulator and rectifier

I come back here for help as I have tried the cb750 forum and not a lot of help there.
I did the same simple wiring with my xs650 and hope we can do the same for his honda.

Im not sure of the alternator on the honda if it is a field excited type or not. By schematics I think it might be. I see a green wire going down to what looks like a brush and then on to frame ground.
I see in the schematics a white wire going down to what I think is the other brush. It comes from the regulator. The alternator has 3 yellow a dark green (ground) I think a white wire. Not labeled.

My question is about the regulator of the vr-115 Having did this on my xs I tied the orange and yellow together and wired them to the 12v hot lug on my fuse block.
But I cant remember where I wired the black and green wire. I think the green went down to the brush but cant remember if it goes to the hot side or ground side.

If using the vr115 and the honda has a white wire sending needed 12v to the alternator then It seems I know I need to use the black and or green from the vr115 to the alternator but I just not sure which one would connect to that white wire.

In fact Im not sure if this 78 cb750 has brushes?: I did some searching and could not find brushes for this bike. It may be a pickup down there that the white and dark green wire go to.

I did some searching here and found a post where RG told how to use the vr115

orange & yellow.................brown (load side of ignition switch)
green...............................green (left outer brush)
black................................common black wire in harness or bare metal on frame.

So im thinking that the green from vr115 would go to the Honda white of the alternator and black go to frame ground.


If anyone can clue me in and help us on his project I would appreciate it greatly.
By the way all you fathers, I hope you have a good fathers day.

 

[cycleranger]

Did you check this thread?
http://forums.sohc4.net/index.php/topic,12465.0.html
Lots of reg/rec info and wiring diagrams in the thread.

The CB750 alternator does not have brushes and is an excited field alternator.
You can also download a CB750 shop manual here:
http://www.honda4fun.com/materiale-documentazione-tecnica/shop-manual

which contains the the factory wiring diagrams.

 

[cruzin]

Thanks cr, I seen your posts over in some honda sites while I was searching. Ill try the link and hope I can figure this thing out. thanks again.

 

[cruzin]

I seen that thread before. With the field excited type what differences would there be in doing this conversion? And they use another type vr regulator.
What year and bike did you do that conversion to?
Another poster there stated that the older bikes had to have some modifications the field wiring needs to be modified he stated:
Doug, the Dodge regulator is better suited as a direct replacement for the SOHC 650 and DOHC bikes, than for the other SOHC bikes. To use this on an 750 or 550, the field wiring needs to be modified, as the stock setup grounds one end of the field coil through the harness, and the reg controls the field current by adjusting the connection to battery +. The Dodge reg controls the field current by adjusting the connection to ground, just like on the 650.
Dave500 suggested a Bosch reg that was pretty much plug-and-play for the older bikes a while back, but it was a bit more expensive than your alternatives. It might be worth the extra bucks for those lacking in electrical expertise?
Can you explain this?
So may be the vr-115 is not a good candidate for this?

 

[TwoManyXS1Bs]

Your Honda's field coil is a non-rotating coil fixed to the sidecover. The rotor is like our XS650 rotor, but hollow inside, and spins around the fixed field coil. This indirectly magnetized rotor spins inside the stator, like our XS650s. The field coil is around 5-6 ohms, and powered by the regulator. Essentially, it's very similar, electrically, to our 70-79 alternators, and RetiredGentleman's VR-115 regulator mod would apply...

 

[cruzin]

Thanks 2M I was hoping to hear good news. In the Honda manual up to 79 they say they have a charging system like an auto. Then in 79 they went back to brushes. So safe to wire it like a xs with the green from the vr115 to hondas white and vr black going to hondas dark green. thanks again. So is the starting clutch spinning? And is the starting clutch part of the charging system? From the picture it looks like everything has wires keeping it from spinning. Very confusing to me. It does not look so simple and glad you showed the picture. I may have cut most of that wiring out But it looks like there will be a lot more to keep than our xs650's

I downloaded the shop manuals and I understand the starter clutch now.

 

[cycleranger]

I seen that thread before. With the field excited type what differences would there be in doing this conversion? And they use another type vr regulator.
What year and bike did you do that conversion to?
Another poster there stated that the older bikes had to have some modifications the field wiring needs to be modified he stated:
Doug, the Dodge regulator is better suited as a direct replacement for the SOHC 650 and DOHC bikes, than for the other SOHC bikes. To use this on an 750 or 550, the field wiring needs to be modified, as the stock setup grounds one end of the field coil through the harness, and the reg controls the field current by adjusting the connection to battery +. The Dodge reg controls the field current by adjusting the connection to ground, just like on the 650.
Dave500 suggested a Bosch reg that was pretty much plug-and-play for the older bikes a while back, but it was a bit more expensive than your alternatives. It might be worth the extra bucks for those lacking in electrical expertise?
Can you explain this?
So may be the vr-115 is not a good candidate for this?

I installed a VR124 on my '75 750.

http://forums.sohc4.net/index.php/topic,12465.msg1193071.html#msg1193071

But the VR115 should work just fine.

Oh, and here's a simplified wiring diagram. Just the essentials.
http://www.hondachopper.com/garage/simple_wiring_diagram/simple_wiring_diagram.html

 

[jetmechmarty]

This guy can help if you need him.
http://www.oregonmotorcycleparts.com/

 

[cruzin]

thanks everyone Ill post back when I get it done, thanks

 

[cruzin]

I checked the simple wiring diagram out. now the question is what are all the wires in 2M photo. Looks to be 10 more than I would expect.

 

[TwoManyXS1Bs]

I wouldn't worry about those, unless you're rewiring the whole bike.
Here's a schematic:

 

[cruzin]

2M those wires in the picture must be needed they look like they come from the starter clutch. unless they are things like neutral light and kick stand switch.I have not been in to one of these motors. Ill look at the manuals some more. The guy Im helping just wants it to run with a headlight, brake and tale light. With kill switch on off switch and another on off switch for lights and a push button momentary switch for starter. Hes going to run a battery but get rid of everything he can. Ill look at bike also and see if I can identify where those wires come out. and where they go. thanks again for your insite and knowledge.
Do I just cut them wires off!

 

[TwoManyXS1Bs]

Wish I could be of more help, but I'm mostly drawing on 40+ year old memories, which are understandably interspersed with other '70s trivia. As the Honda models progressed thru the years, they became more technologically dispersed and complicated. I never got into the '78 CB750. They were still new, not breaking down requiring serious work. And, that's about the time I jumped ship.

I was thinkin' that it would have been easier on you if I had simply 'erased' that distracting harness glob from that pic...

 

[cruzin]

I looked at the wires coming out of the alternator area (2 groups of wires) and one is the 3 yellows white and green and another one coming from the starter, I didnt see much more than that. I think its going to be pretty straight forward like the xs. Ill probably just keep the plug that hooks to the headlight in the bucket and rewire everything back from there. On this guys bike someone made a steel side cover for the left side and I think we came to the agreement that we would mount 2 off/on toggle switches and a push button for start in it and leave the wires long enough to remove it without undoing the wires.

 

[cycleranger]

2M those wires in the picture must be needed they look like they come from the starter clutch. unless they are things like neutral light and kick stand switch.I have not been in to one of these motors. I'll look at the manuals some more. The guy I'm helping just wants it to run with a headlight, brake and tail light. With kill switch on off switch and another on off switch for lights and a push button momentary switch for starter.
He's going to run a battery but get rid of everything he can. Ill look at bike also and see if I can identify where those wires come out. and where they go. thanks again for your insight and knowledge.
Do I just cut them wires off!

There's a clutch safety switch that is wired through the starter safety diode.
It's tied into the neutral indicator switch to prevent the starter from working unless the clutch lever is engaged or the bike is in neutral.
I believe on the '78's there is also a relay to bypass the headlight when engaging the starter. There is no switch for the headlight, it's intended to be always on.
To do what your friend desires you're probably going to have to pull the entire harness to do the modifications.
I would advise against just hacking the existing harness until you have traced all the relevant wiring. Unless you just want the rebuild the harness from scratch, in which case you can use that simplified diagram I linked to earlier.

 

[cruzin]

thanks cr Yes he just wants a simple basic wiring. just 2 toggle switches and push button switch to start it. and a kill switch. thanks all who have helped to clear this up in my mind.

 

[cruzin]

We are to the point I could start wiring the cb750. I have used a vr115 with a 50amp 3 phase rectifier. Used the 3 yellow, 1 white and the green wires. My issue at the moment is it won't roll the motor over. I hear what sounds like the Bendix roll over but it either does not engage with what it's supposed to or the charged weak battery won't allow it to engage. Just a wirrring sound. I did not do anything with the green and red or the blue and red wire. The go down in the same loom as the yellow white and green. Could this be something to do with those spoken starter clutch?
I just have a power wire active and push button for start.
Any suggestions

 

[TwoManyXS1Bs]

Don't know about your later starter clutch, but the early models used a sprag clutch. My fix for those was often just a simple cleaning of the one-way rollers and the race they grab onto. Some oil additives would make those surfaces too slippery for them to grab. The cleaning fix included a very light sanding with very fine sandpaper, just to get the glazing off the metal. Worse case would involve replacing the rollers and gear...

 

[cruzin]

The owner has a new battery I think Ill try before opening things up. The electric start worked when He brought it over to us. Hopefully the new battery will solve the issue. thanks 2m. This may be a later one its a 1978, last year for the sohc.

 

[cruzin]

I was wrong, the starter did not work proper when the bike was cold. It always just spun and not engaged the flywheel. So I guess we look at the starter clutch. I ordered a puller the other day.