86 CB700SC No Start

[295566]

History: Trying to revive my pops' bike that's been sitting for ~2 years. He used to ride it somewhat regularly, but coming home one day it suddenly died on him. I picked him up and we determined it wasn't getting any spark. Never really worked on it after that and it sat.

Fast forward to a few weeks ago and now I have a garage... so I picked the bike up from him trying to get it back on the road. Forks, both brake and clutch master cylinders, and carburetors have all been removed, cleaned, and rebuilt. However, the initial problem of no spark still persists.

Pops put a new battery in a few months ago but that did not solve the problem, still no spark. When I got it, the bike would crank over no problem but no spark. However, since taking possession it no longer does that. It will spin over no problem by shorting the terminals on the starter relay, telling me the battery and starter are both OK. Swapping out another starter relay doesn't change the situation.

Currently hitting the start button on the bike nothing happens. The headlight turns off, as it should, telling me that the signal is being sent, but somehow not to the starter relay.

So here's where I'm at: I know the battery, and starter are good. I'm assuming the starter relay is good, as it's brand new, and I've tried two others (OEM Honda used that were lying around) that don't help. I'm also assuming the starter switch on handlebar is good, because it kills the headlight when start button is pressed, implying it's working. Also tried another OEM Honda one lying around, no change.

Anyone familiar with these kinds of bikes can point me to where to look? Not sure if the new, no-crank is the same problem as the no spark that initially mothballed the bike, or if they're independent.

TLDR:

• No crank when start button pressed, rank but no spark when starter terminal shorted.
• New battery, new starter relay.
• All lights and horn work, all fuses ok.
• Headlight goes out when start button pressed, but no click from starter relay or crank.

 

[Maddevill]

Does it have a sidestand switch? If so, bypass it, and see if you get spark.

Mad

 

[295566]

No sidestand switch on these bikes, only neutral and clutch safety switch. Both appear to be working (neutral light comes on in neutral gear, or when clutch is pulled in).

 

[bobl]

Check the signal from the starter switch at the solenoid. Because the light goes out, doesn't mean the signal is getting to the solenoid. There are two different contacts in the starter switch, one disengages the light, the other sends a signal to the starter. You can also check by applying voltage and a ground to the small wires on the solenoid. Start by using a voltmeter on the positive side of the solenoid, and pressing the starter button. Voltage should arrive when button pressed.

As for no spark, you have a signal generator, wires to the ignitor, and wires to the coils. Have you checked the fuses. Do you have a service manual and wiring diagram?

 

[auntiebling]

i'd take apart and clean the switch pods. honda likes to send a bunch of current through them and they frequently corrode/erode causing all manner of issues.

also check grounds. maybe even add a few (even though it isn't italian....)

 

[295566]

Funny enough, when I got the bike one of the main grounds wasn't even connected. That has since been corrected. Can't see any others missing, but I will add systematically going through and cleaning all contacts to the list of to-do's.

 

[auntiebling]

i did a little digging and it looks like that bike has electronic ignition, which is good because i hate points because i don't understand them but i digress

it has what is effectively a factory electronic conversion of a points system with hall effect sensors, it's called the "pulse generator" in the manual. that era of goldwing (a model near and dear to my heart) uses a similar setup and the pulse generator is known to give up from time to time. sucks that they're NLA new

https://www.partzilla.com/product/honda/30300-MJ1-770?ref=8489043c84c37c3956c93d927ccc56174a19af3c

those are worth a test. check the coils too, it's unlikely they both failed at the same time but i suppose it could happen.... which is what bobl said more or less

 

[bobl]

If there is no signal to the solenoid, I would first check the starter switch on the handle bar. If it's been sitting, the sometimes corrode. I fixed a friends cb400f that had no headlight. Checking, it turned out to be that starter switch all corroded. Electrics on those older models are a lot simpler than the new stuff.

 

[295566]

Failure of the coils wouldn't cause the engine to not crank over anymore though, right? My theory with the no-crank issue is: either a bad connection/bad wiring somewhere, starter switch is bad (tested with another but no go), or relay is bad (unlikely, as brand new, and tested with 2 other units, no go).

As I understand, starter circuit is relatively simple. Battery > Starter Solenoid > Starter motor, and handlebar switch > starter solenoid.

We know the battery and starter motor are good, so the fault has to lie somewhere else. In this case, either starter solenoid (as stated, unlikely), handlebar switch, or wiring.

 

[auntiebling]

coils wouldn't affect cranking correct.

 

[motomania2007]

On most bikes there are at least two circuits that must be in the proper state for the ignition to produce a spark.
One circuit closes the starter circuit and makes the starter spin and therefore spin the engine over.
A second circuit also turns on the ignition ie provides power to the igniter box or engine control unit or whatever you want to call that ignition box.
Often times there is yet a third circuit in the ignition switch that removes a ground that is the kill switch for the ignition system that is there to prevent the ignition from producing a spark.
I don't have a wiring diagram for this particular motorcycle so I'm not sure exactly what it has but it's going to have at least two circuits and both of those circuits must be functional and in the proper state for the ignition to produce a spark.

To summarize, You can hotwire the starter solenoid like you have done and the engine will spin but it will produce no spark because you haven't also turned on the igniter then actually produces the spark.

So my suggestion is similar to what's already been suggested: check the ignition switch and the connectors to it to make sure that it is in the proper states when the switch is in the proper positions and also check the engine cutoff switch I either kill switch on the right switch box and make sure that there are no corrosion issues and that the switches are making the correct electrical connections and that all the electrical connectors between the engine cutoff switch and the ignition switch and the igniter box are all free of corrosion and are still good solid connections

 

[msethhunter]

You have multiple problems.

Pulse generator has gone bad. That should fix the spark. Check to see if you're getting power to it. I bet you are. Also check if you're getting power to the coils/coil?

No crank is probably wiring, judging on everything else you've tried.

Do you have a wiring diagram or the manual?

Pull the wire off the starter and see if you get voltage there when you hit the start button. If you do, run a jumper wire to it from the other end to see if you can bring it to life. My bet is with the age of the bike, and trying to start it with no spark has given you high resistance somewhere by getting a wire to hot.

Sounds like you're headed down the right path, but a diagram with a manual would be a huge help.

 

[295566]

Wanted to circle back to this. I went through and systematically cleaned every ground and electrical connection, including connectors and fuses. Bike cranks and sparks strong now!

Unfortunately waiting on carb parts, as I was unable to remove one of the pilot jets and it broke inside the housing, it was so badly corroded and nasty. Hoping to receive that Friday, and reassemble that weekend.

Will update when I get the bike running properly. :cool

 

[auntiebling]

sweet
while you're waiting, take apart the stator to harness connector and clean it. EVERY honda has a problem with this connector, as to many other manufacturers, with corroding/heating/melting/dying. if you are game and confident in your skills, just chop that connector out and solder the leads directly.

 

[Jalopyshoppe]

I forget which years do what, but some Hondas will crank with the kill switch off, and some won't. Perhaps you have a bike that falls in the latter category. Even though the rest of the circuits are good, perhaps you have a bad handlebar kill switch. That would explain no spark and no crank.

 

[295566]

Yeah I read that this year/model would do that. Not sure if that was the case, but cleaning all the contacts seems to have corrected the problem. I also rebuilt the handlebar switch.

It was interesting to note that all the connections looked good and felt solid. There was no visible rust/corrosion, or loose connections. I know corrosion can be inside the wires/insulation too, so maybe it just broke loose there... don't know. Hoping this corrects the problem long-term, and won't rear up in the future. At least if it does, I'll know where to start.

 

[Tom G]

As auntie bling stated, make sure the connections to the stator are good. This will bite you in the future. If the plug doesn't look clean but rather heated up fix it or it may fail when you least want it.

 

[ST Guy]

sweet
while you're waiting, take apart the stator to harness connector and clean it. JUST ABOUT EVERY BIKE has a problem with this connector, as to many other manufacturers, with corroding/heating/melting/dying. if you are game and confident in your skills, just chop that connector out and solder the leads directly.

Corrected.....

However, don't just solder. Crimp using a butt connector. Then solder. Then insulate with heat shrink.

 

[Jalopyshoppe]

Corrected.....

However, don't just solder. Crimp using a butt connector. Then solder. Then insulate with heat shrink.

This is a tangent, but I'm curious why you would solder at all? We had an EE on a race team when I ran the 25 hours of Thunderhill. He specified crimp connections only with glue lined shrink wrap.
His reasoning was that crimp connections have the same conductivity as solder, but the solder connections create a stress riser at the joint and are not recommend in any high vibration environment.
I'm sure the shrinkwrap is ample strain relief, but I have moved to this method on the cars and bikes I build and have had great results.

 

[auntiebling]

^^^
this is a What Kind of Oil do you like discussion. TONS of examples of Crimp Only in various industries. solder only (lineman splice style) also works really well.

I don't mention shrink wrap or whatever because it's like, DUH, you need to insulate it if i have to explain that you shouldn't be doing wiring.

ST Guy likes belt AND suspenders and that's cool too. he also likes molybdenum on his toast!

i tend to be solder only because i rarely have the right crimp fitting on hand and i'm in a hurry, usually