1981 cb750k starting issue.

[barelycompetent]

Hi all, brand new to the forum and I have tried to search the forum to see if anyone else has had the problem Im having but I havent had any luck finding information. I do apologize right off the bat if this question has been asked and answered before and I missed it in my search.  So here goes, I have a 1981 cb750k that was running when I bought it.  Over the course of the last two months I have been tearing it down and converting it into a cafe racer, however I have not had to do anything with the wiring so that is all stock.  My bike was starting and running until one day I was cranking on it to start it, and I let off the starter button, and when I hit the button again nothing.  No click from the solenoid, nothing.  All of the lights and indicators came on, neutral light, oil light, headlight, and when I pushed the starter button the headlight went out as its supposed to, but again I got no click from the solenoid and not a peep from the starter.  I laid a screw driver across the solenoid and the starter fired right up.  I assumed then that it must be the solenoid, so I found a replacement(only 10 bucks so Im not out that much) put the new solenoid in, making sure to hook the wires up as they were on the old one, turned the key, all lights on, hit the starter button and once again nothing.  No click from the solenoid and no starter.  Jumped it across the solenoid and bang the starter fired.  I guess its possible I could have gotten a bad starter solenoid, but I dont know.    My question is, where do I look, and go from here?  I have read somewhere that the connections on the ignition switch can sometimes be intermittent so I checked those and cleaned them with wd40, reconnected them and still the same results.  Could it be possible that the kill switch is to blame?  Its in the run position when I am trying this but if the switch itself is bad it might not be making contact.  Has anyone else ever had this problem?  Any help is greatly appreciated as its starting to warm up in my neck of the woods and the riding but is starting to bite again!  Again if this question has already been asked I apologize for asking again, and if you could point me in the right direction I would greatly appreciate it!  Thanks in advance!

[TOOLS1]

This is so simple. Your bike is protesting the fact that you are turning it into a cafe racer.
It's probably your starter button. These go out all the time. Take the wire off the solenoid that comes from the button. Hook up a test light to it, and push the button. The light should come on. If it doesn't your button is bad. If it does then your solenoid is bad.
TOOLS  

[barelycompetent]

Thanks tools lol I was wondering if someone would mention the cafe racer!  That was one of the first things I did with the old solenoid, and the new one, I get all the proper signals when the button is pushed, and both of them fire the starter when I jump across the solenoid. I guess its possible I could have gotten a bad solenoid from the manufacturer but I was trying to narrow down if there was anything else I should check before spending more money on another replacement lol. Thanks for the response, any other ideas I should look at and check?

[TOOLS1]

I'm not understanding what you are saying here "That was one of the first things I did with the old solenoid, and the new one." Did you check to make sure that you had power coming from the button, or just jump across the solenoid? It is very common for the button to go bad, and very rare for the solenoid to go bad.
TOOLS

[barelycompetent]

Sorry for the confusion, yes I had power from the switch on both the old and new solenoid.  Power is getting to the solenoid it's just not going out to the starter unless its jumped across, yet all my lights come on when the key is turned.  That's what's got me scratching my head as to what else it could be.  

[barelycompetent]

I meant to say button not switch, I have power from the button as well as the switch.

[TOOLS1]

Try using a jumper wire from the + battery terminal to the solenoid terminal that the starter button wire connects to. If that does not actuate the solenoid then it is bad.
TOOLS  

[barelycompetent]

Ill give that a shot but sadly I won't be able get my hands dirty in the garage for a few days, to much going on right now.  Appreciate the help, I had a buddy locally that thinks its the kill switch, I don't want to throw money at a problem if I'm not certain what it is.  Do you happen to have any suggestions on how to test the kill switch?  Just trying to think a couple steps ahead in case your suggestion doesn't fix it.  Again thanks for the info it's appreciated and like my signature suggest I know just enough to get me in trouble lol.

[TOOLS1]

If you are getting power through the starter button then your kill switch is OK.
TOOLS

[Cabreco]

I'm going to take a shot in the dark here, because sometimes the simplest thing cause problems.
You said you've been tearing it down, by any chance are you in gear?
My 81 won't engage the starter unless it's in neutral or the clutch is pulled in, although all the lights work.

Just throwing it out the just in case you may not have noticed you're in gear.
It's the little things that give you the most grief.

[barelycompetent]

Thanks tools, appreciate the advice and with any luck I will hopefully be able to get my hands dirty tomorrow.  As far as being in gear, yes I am in neutral.  The neutral light comes on, and I have tried multiple times to put into first gear, second gear, back into neutral, in gear pull in the clutch and try to start it, jiggle it, make sure its in neutral and still nothing.  Recently after putting it into gear and back into neutral several times I was able to hit the button and make it fire but as soon as I let off the button it went back to nothing.  Could it maybe be the neutral switch?  Giving me a reading of neutral but actually being in gear?  The bike is on my lift so when the neutral light is on I can move it back and forth somewhat likes its actually  in neutral.  I dont know, Im going to give tools suggestions a try and see what that does, but this thing has me stumped and getting frustrated lol, at least when I get fed up with the bike on the lift I have my custom chopper I can jump on for some two wheel medicine so I have that going for me.  Thanks again for the advice and suggestions, gonna see what happens!

[LukeM]

Nothing prevents you from taking out the battery, starter, and solenoid out of your bike, wiring it up with some stout wire (10 gauge should do), and making sure these pieces work as intended.  You'll need a suitable switch to act as your starter switch for the "low side" of the solenoid, and some wires for the "high side" of the solenoid and starter. That way you'll know they are good, and if they are, the problem lies elsewhere.

On my '79, the engine would start in gear as long as the clutch is pulled in.  It would also start if the trans was in neutral, and the clutch is either pulled in or let out.  Not sure about the '81 model. A good wiring diagram or schematic would help.

Good luck.
Luke M

[barelycompetent]

Thats a good idea too Luke.  I do have a pretty decent color wiring diagram that shows one of the wires going to a diode and splitting from there to a clutch switch. Before when it was running as long as the neutral light was on it would start, if it was in gear with the clutch pulled in it wouldnt.  If it was in neutral it didnt matter if the clutch was pulled or not it would start.  I dont know where the clutch switch is though as it doesnt give me a location on my diagram.  Could that be my problem all along?  Even though before it was starting no problems as long as it was in neutral?  Maybe its the diode and clutch switch?  I dont know, have to locate them first, is there any way to test them?  I appreciate all the advice, its giving me directions to go, hopefully I can locate the problem and square it away.

[barelycompetent]

Just an update, I tried using the jumper wire from the plus side of the battery to the starter button wire on the solenoid and got nothing, it didnt actuate the solenoid.  Guess that means I have a bad solenoid, so looks like Im going to be out another 10.50 for another replacement.

[barelycompetent]

Well the bike is starting and running again!  Turns out it was the clutch switch.  Thing is I never suspected it because when I bought the bike as long as it was in neutral it started and ran whether the clutch was pulled in or not, so when it quit cranking I didnt suspect the clutch switch.  Turns out it is pushed into the housing just a hair to far and not allowing the switch to fully engage.  I moved it out just a touch and bang fired right up.  Thanks for all the info and help guys I do appreciate it, one more question though.  Do I need to replace the switch or just bypass the whole thing?  The switch works but I have a feeling its going to cause me alot of headaches down the road.  What would you guys do if it was your bike, bypass it or leave it be?  Thanks again for the info.

[sgtslag]

The clutch switch is a safety feature.  I would replace it.  Cheers!

[barelycompetent]

Thanks Sgt!  Do you know where I can find a replacement switch?  Do I need to buy the whole clutch perch or can just the switch be purchased?  The switch itself actually still works it just seats to far into the housing to allow the switch to engage when the clutch is pulled in.  I do have aftermarket grips on the bike that my buddy that was helping me thinks are thicker then stock and not allowing the clutch lever to pull in far enough.  Maybe I should take my angle grinder to the backside of the lever and shave it down a bit.  I dont know, just have a feeling that once I start putting some miles on the bike that the vibrations will cause that switch to jiggle out of place just a touch and Im back to square one lol.  I appreciate the info and advice, learning alot from these forums!

[TOOLS1]

Honda still sells the switch. It just pushes/snaps into the clutch perch.
TOOLS

[barelycompetent]

Thanks Tools, gonna look there.  I did a search yesterday but was unsuccessful in locating one, so I will check with Honda and if they are reasonably priced I will replace it if not then its bypass and go lol.  Thanks for all the great info and suggestions, it is appreciated!

[shinyribs]

The clutch switches slide in from the lever side. The wires feed in first. Maybe since your switch is good,but you cant get full travel out of it,you could just shim it out somehow. Just a thought. I'm cheap like that.