Topic: Persistent CB750 starter button issues

[cshanek]

BryanJ, yes it was.

[bryanj]

OK then, next test is disconnect all wires to switch and using the ohms setting on your multimeter see if the yellow/red connects to the switch body when the button is pressed, if not find which other wire the yellow/red connects to with button pressed

[gp_st3]

I recently had problems with intermittent starter operation on my K4 - after lots of studying wiring schematics and checking with multi-meter etc., I ended up bypassing the saftey logic unit by un-coupling the Red/Green connector in the headlamp bucket and connecting the (Red/Green) wire coming from from the handlebar directly to ground. Now it works as the earlier K type where pressing the button grounds the Yellow/Red wire without going back through the safety unit... worth trying?

[cshanek]

Quick update on all of this, I have been working with 05c50 over the past week or so, and ran some tests last night on the ignition switch. Initial impressions are that there is an issue with the switch. I will post updates as we find out more.

[cshanek]

@#$@!$!

Still no dice on this, thinking about punching a few things and just ripping every thing apart and starting over. I'm also contemplating launching the 2 switches I purchased from vintage cb750 into #$%*ing orbit. I've had great help from patient people but I'm still where I was (albeit with a better functioning switch) when I wrote the post. It's absolutely #$%*ing ridiculous that I have not been able to work through this problem considering how simple the electrical system for these bikes are. 

[Grabcon]

Okay. I had the same issue on my 1976 CB750F. The difference is I have all original switches and wiring. I chased this for some time without resolution. Finally I sent a note to Honadaman and after a fairly long response explanation of what the issue is and a fix,  he sent me a schematic of the fix. It is fairly simple and only costs a couple of buck. Install a replay that turns the headlight off when the starter button is depressed. I works flawlessly. Never an issue since I have done this fix.

Not sure if you have tried this but make sure it runs. Mine did start with the kick start.

Attached is the schematic that Hondaman sent me. Hopefully he won't get mad for sharing.

[bryanj]

This is one of those problem that takes 30mins to fix if you are experienced and sat there but impossible via text.

If you have a decent multi meter, are willing to follow specific instructions and report back please PM me and i will start from scratch with you-----not forgetting the time difference from being oposite sides of the pond. At the moment i am awaiting the renewal of my truck licence after a heart attack so have time on my hands.

[cshanek]

I've gone through a handful of multi-meter and continuity tests now with 3 people, all very experienced. I will certainly reach out to you if I do not get anywhere.

Paul, there is a possibility that some of our tests toward the end of our session had garbage results, as I found out last night that my 5A fuse had blown (probably my fault when plugging and clamping stuff during test). I replaced it, and will sit down with a cooler head and some alcohol this weekend and try again to work through this. The race is on Nasa ... will I figure out the problem before we colonize Mars?

The Vintage CB750 people's response to me was ... "we've sold 500 sets of these things specifically for the 76, and we have never heard of a problem". That's a pretty cool feeling reading that. Reminds me of a time I was having a tooth drilled on, and the bit hit a nerve. I jumped back in the chair, grabbed the dentist's arm, he stopped and looked at me and said "no, that nerve is under, that should not hurt".

[tlbranth]

pj said it. Trying stuff is just a waste of time and you learn nothing. You need to understand how the switches work, where the wires go and what they are for. When you figure it out, draw an accurate wiring diagram so you'll be able to fix things in the future. Don't let this thing confuse you. It's really a pretty simple setup. With a decent VOM you can figure out what's going on. Wish you lived closer, I'd help you out.

[Mantree]

Offer still stands if you want to trailer it up the fort Collins I will sit down with you and we can get it running.

Sent from my SM-G900V using Tapatalk

[cshanek]

Update:

Ding dong the witch is dead ... or she is dying at least.  I was able to get the starter button on the right handlebar switch to work last night. I will provide a couple of steps regarding that process below, but first I want to thank 05c50, bryanj for their patience and input, as well as those that offered local assistance.  Hopefully this post will save someone from experience the same headache/heartache. Now on to the meat and potatoes.

Lesson 1: First, if you buy a right handlebar switch from VintageCb750, test the switch for appropriate resistance. In my case, for their 76 cb750 K6 switch, pressing the start button should close the circuit between the red/yellow and red/green wires, so that a multimeter would have a low resistance reading. Both the original and replacement switches I received from them had open line readings on my multimeter when the button was pressed. Part of my problem is that I applied Occam's Razor and assumed that the likelihood of me getting 2 crappy switches from them was very low, when in fact that is exactly what happened. I re-soldered the connections of those 2 wires last night, and with the step below, everything worked fine.

Lesson 2: BryanJ had me test voltage readings at the starter solenoid as well, and I am not sure how or why this happened, as I also bought a new 76 harness from VintageCB750, but the green/red coming off the handlebar switch had to run to a hot connector in the headlamp bucket (black in my case). For some reason the green/red on the harness did not have any voltage.

Lesson 3: When things went South in spectacularly confusing ways I just flailed around, burned fuses, and attacked the problem with a brute force approach instead of breaking it down logically into smaller, easier to test/verify sets if test (as many of you mentioned).  Oddly enough I am usually pretty good and handling similar issues not related to motorcycles so I will have to use this is a learning point. Part of the reasons I love my 73 and 76 is because of the beauty of their simplicity, which is apparently still plenty difficult enough for me.

I've emailed this information to the VintageCb750 people who have been quite nice about all of this, so perhaps they will post updates to their instructions if warranted. 

My headlamp is still dead, but I am confident that will be an easy fix.   

[Mantree]

When I inherited my bike the wireing was so bad I ended up rewiring it and it ended up more like a old hot rod than what it originally was becaus I wanted fo run heavier wire but less wires over all

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[bryanj]

As I said privately to the original poster this proves a statement i was given 50 years ago when an apprentice :-
"Just because it is new it does not mean it works properly!"