I've bought another project CB700SC

[ThePowster]

Evening fellas.

Ok so I was a member of this forum before it updated. I bought a 1985 CB700SC but it needed a new cylinder head, so I broke it down into bits and it was going to be a project.

Now fast forward to current day and I saw another one for sale so I snapped that one up too lol. This one is complete but it's got a whopping 74k on the clock.

Anyway the bike started but it would not rev clear. So over the last few weeks I've had the bike in my living room and I've done the following:

1. Drained bike of fuel and replaced with fresh.

2. Removed and cleaned the carb and jets.

3. Replaced old spark plugs for new (ones that were in it were black with soot and we're ngk dpr7ea and I've replaced them with ngk DPR9EA-9 ones.

4. The wires to the CDI were full of black like tar so I've cleaned that up.

5. Replaced all fuses with correct amp 250v glass ones.

So tonight I couldn't wait any longer, and after a few tries she fired back into life and sounded OK, but I have what must be electrical gremlins.


1. The rev counter stopped working and the neutral N indicator vanished, then it came on and went off again. I'm not sure what is responsible for that?

2. The bike revved higher than before, maybe 6k but it feels it's starting to slow down just revving it, and I can hear what sounds like tiny backfiring in the right exhaust.

3. The headlight didn't come on nor did the indicator for it on thr clocks. Odd as it was working before.


I feel I'm not a million miles away from having a running nighthawk, but the bike still has issues.

Now back of the headlight all the wires have been butchered and I do not know what wire goes where.

The rectifier wiring has also been cut and bullet connectors added and again I'm not sure they have the right wires going to the right coloured ones.

I cleaned the air filter but it feels blocked to me. I can't blow through it. But I'm considering dropping a K&N in the airbox with a custom lid.

Anyway that's my story. That's where I'm at. I think I'll start at the front of the bike, the headlights and work my way back.

I'll take some pics and see if anyone can help. The manual electrical diagram really didn't help me at all.

Cheers

[Larry Fine]

Yes, this is the place. Someone here has access to most of the old forum.

I happen to be an electrical contractor, and I know Honda wiring, so ask.

[mollusc]

There's also a wiring diagram in the back of the Honda Service Manual, which you should have anyway -- it's the most important tool you can own for this bike.

I know that there's an aftermarket airbox lid available so you can use a pod inside it, so your idea there seems like a good way to go.

[ThePowster]

Afternoon chaps

OK first things first, here is my second nighthawk (the other is fully broken down into tubs).




I paid £1,000 for her as a bike that needed restoration from being stood, but she needs a little more than that and with 74,000k miles on the clock I'm not expecting miracles, but I have been wanting to ride one of these for years.

Speaking of riding lol I have just got back from a cheeky blast on it. No road tax, insurance or MOT but the temptation was just too strong, so I nipped it down the duel carriageway. Wound her up to the ton (100mph) and bought her back.

The clutch is dragging, once bled it's ok for a bit then air must be getting in. The revs are slow to come back down and are idling around 3-4000rpm but when it sits around 1,000rpm it stalls.

I don't have any air filter in the air box at the moment as the one I have seems to be totally blocked.

Great to see we have an electrical guru onboard! The electrics on my bike are shot. Every part of the look has been cut and sliced into and bullet connectors going everywhere.

Behind the headlight for example, there are orange wires, male and female, many of and I don't know which one goes where. I have spent ages going through all permutations and it's the best it's been but it's still not right. Example, front indicators light up and are on all the time, when I indicate they flash but then one goes out and the other stays lit. Maybe it could be the switch.

The best thing I can do is look at this one step at a time and one question at a time with lots of pics, that way we can start to rebuild this forum for the next chap who comes across this problem and we can have it documented.

Right now I am just smiling because I had a go and got away with it lol but I don't do that again until she's fully road legal.

Right I'll find the relevant categories and go ask my questions and link to what I by and pics of new parts installed.

Great to be back!

Cheers.

Matt.

[Bob H]

Nice! what was your old forum name?

[ThePowster]

Thanks Bob. I think it was the same as I have now, ThePowster?

[Bob H]

OK, cool. The 700SC is amazing.
I love my late model 750, but have had bikes with shaft drive (Yamaha 850 triple from 1980, Yamaha 750 Seca 1982) and your bike has it all.

The only thing that would keep me up at night is the starter issue - when that goes you have to split the cases on the 700S and replace the connecting chain with the late model 750 starter chain I believe (it is wider and stronger)

[mollusc]

Great find!  Looks like it's very well maintained.

[Northern Rider]

Nice looking bike. Does anyone know if a 700 NH headlight fairing would fit a 96 750 NH? Thanks.

[Larry Fine]

Great to see we have an electrical guru onboard!

I don't know if you mean me, but I do know the wiring and colors.

Let us know when you're ready to get started with it.

[Larry Fine]

Nice looking bike. Does anyone know if a 700 NH headlight fairing would fit a 96 750 NH? Thanks.

No, but if you can find a clean one, a Vetter Rooster looks good on an NH750. This is mine before I switched to a WJ5:

[mollusc]

The 700S fairing would not fit the CB750 unless you changed the entire instrument nacelle.

[Northern Rider]

Larry thanks for the pics of your Vetter, I will check it out.

[ThePowster]

Great to see we have an electrical guru onboard!

I don't know if you mean me, but I do know the wiring and colors.

Let us know when you're ready to get started with it.

Cheers Larry. My wiring is a right mess behind the headlight.

My bike starts and sometimes the headlight is on and sometimes it is not. Also the front indicators are both lit, until I indicate either left or right and when I cancel one goes out and the other stays lit.

Behind the headlights there are loads of orange bullet connectors male and female and I don't know what goes where, but I'll take some images when I next can and show you where I am at. It's a right mess and the wiring was butchered before I got the bike.

[Bob H]

...the wiring was butchered before I got the bike.

Take photos of the existing scene before removing anything, create a diagram, and start over.
Hopefully you have a manual with wiring diagram.

Your focus will essentially be the lighting, turn signals, and maybe horn circuits (only).
so it's not like rewiring the whole bike.

When I did my late model 750 wiring, I did the common mod of using a RELAY for headlights. So you aren't running all the  electricity through switches. The ignition turns on, relay active and "wham" you have full power straight from battery to relay to headlights. Same for the horn, relay puts full power to a Fiam or Steble / Air horn rather than going only through the horn button wiring.

Also the opportunity to do flasher upgrade to one that can handle LED signals without hyperflash.

I got my relays and wiring from this guy https://cycleterminal.com/
His site appears to show he is swamped or not making some things, but the images will clearly show you the process and you can create the relay wiring yourself. http://www.cycleterminal.com/horn-kits.html

He made wiring relay kits for several of us on the old forum, and he does really clean and solid work.
His page on the use of relays is helpful http://www.cycleterminal.com/accessory-relays.html

He used to have a page dedicated to headlights, but the link no longer works (the one that says H4 bulbs).  Basically it is like the horn relays, but has a thing that you plug the headlight into (rather than a spade lug for a horn). His kit for headlights had 2 relays, one for low, one for high. 
I got a headlight bulb (LED) made for a Jeep that was over $100 just for the bulb, and it allows high and low beams to be on simultaneously.