Need some troubleshooting tips

[Larry Fine]

I recommend starting with basic electrical troubleshooting. First, you should use an automotive probe-type voltage tester, not a volt-meter. It uses enough current to expose bad connections, and you can also use it to check for grounds by clipping the wire to the battery positive terminal or a nearby hot terminal.

Second, check for voltage at both terminals of each fuse. The metal dots beside the number are there for this purpose. Also, there should never be voltage across a good fuse or a switch in the closed (on) position, nor from hot to a terminal that should be hot, nor from ground to a terminal that should be grounded.

[kingston73]

Ok, sorry for not being able to explain things well.  Talk to me like I'm 5, I have a voltage tester that lights up.  I'll summarize as much as I can and hopefully be able to figure out whatever info you all can give me.

Bike starts and runs.  However it seems like a couple times the start button didn't do anything.  I have only sprayed electrical cleaner on the inside of it and don't know what else to do.

All lights work except headlight and high beam warning light.

All fuses are good.  With all fuses plugged in there is 12 volts to each. 

As I said, I have a voltage tester and a multimeter but I don't know what to do with either. 

I've read a lot of threads with suggestions like "check the start switch, check the high/low beam switch" but I don't know what exactly to check.

When using the multimeter to check voltage to the headlight plug it consistently reads 0.15.  I don't know how to check the ground?

[Larry Fine]

Do we live near each other. Where are you?

Do you have a wiring diagram for the bike?

It would make it easier for me to help you.

I will message you my number if necessary.

[Bob H]

...couple times the start button didn't do anything.  I have only sprayed electrical cleaner on the inside of it and don't know what else to do.

All lights work except headlight and high beam warning light.

The following link is for a different Honda motorcycle forum - but appears to be your symptoms and likely solution as Pete pointed out earlier on this thread.
Please read the following thread from start to end, and you will see a pattern of what is considered a common occurrence

https://www.nt-owners.org/forums/threads/strange-behavior-from-headlamp.9261/#:~:text=Your%20starter%20switch%20contacts%20can,It's%20pretty%20common.

Your starter switch contacts can get dirty and will not keep your light on with the start switch released. It's pretty common. Sometimes the switch is sticky and does not fully release on its own....a spring has to push the switch button fully out. It wouldn't hurt to push the starter switch in and gently pull it out without first turning on the ignition to determine if the switch's spring is fully pushing the button out when it is released. Exercising it several times can sometimes help contacts make a better contact, but most likely the starter switch will need to taken apart to clean the contact surfaces.

Also the fact that your starter switch is also intermittently not cranking the bike, in ADDITION TO screwing with your power to headlights - seems to be the low lying fruit. Take the switch apart and clean it as others have done in that thread. Not just spray it - take it apart and physically remove the oxidation & crud that is causing the issue.

When using the multimeter to check voltage to the headlight plug it consistently reads 0.15.

Be glad that you are tracking down the issue, don't be frustrated or confused. This is just a CONFIRMATION that the voltage you see at the fuse is NOT MAKING IT to the headlight plug.

Good. Now you have narrowed down the region where the electricity stops making it's way to the headlight.
If the theory of crappy contacts in the starter switch is correct, then you are seeing a less than one volt reading because of the switch that needs to be thoroughly cleaned (or replaced if you find a used one better than the one you have).

If that doesn't fix it, then you just keep narrowing down the possibilities.

[kingston73]

Thank you for all the help.  After reading through that thread I took the right side starter/run/stop assembly apart and tried to thoroughly clean it with electric spray.  I also took the headlight out and sprayed each connector inside as clean as I could, unplugged and plugged each connector as I went.  I'm not sure what exactly I did (i'm guessing it was probably the starter switch) but after all that I have a working headlight now.

Now my next problem is back to the carbs.  I cleaned them and replaced the jets and bowl gaskets and it now starts up very easily but it is still leaking gas.  It looks like it's leaking from the fuel delivery tubes (#1 and #5 in the diagram).  Hopefully it's just an o-ring or 2 that need replacing.

carb diagram

EDIT:  another thought I had, I replaced the floats and the valve connected to the floats, could the new float valves possibly be the wrong size and be causing the leaks?  It looks like the fuel is leaking from above the bowls and it only leaks when the petcock is turned on and the motor is running. 

[Larry Fine]

Those O-rings usually leak because the rubber shrinks when it dries out.

Sometimes, they'll swell and seal when they soak up gas, but not always.

It only leaks when the engine's running because the vacuum valve works.

[Bob H]

... after all that I have a working headlight now.

Congratulations, well done.

...It looks like the fuel is leaking from above the bowls and it only leaks when the petcock is turned on and the motor is running. 

If you have a mity vac, put very slight suction on the petcock with some spare tubing (the needle barely moves to register amount of vacuum and that is enough to open the petcock.)
If you don't have a mity vac, you can use a syringe (very slight vaccum, don't pull hard).
If nothing else, get a length of vacuum tubing (1/8" ID typically) and suck on the end, very light vacuum - fuel will flow.

Watch like a hawk for where the gas is coming from. Wipe clean and watch again. Establish if it is from the fuel supply tube connecting each of the 4 carbs, or an overflow of the float bowls (not sure where on your model - but you are seeing gas - so it's not just pouring into the engine)

Those O-rings usually leak because the rubber shrinks when it dries out.

Sometimes, they'll swell and seal when they soak up gas, but not always.

That is EXACTLY what was happening on my 1993 NH 750, and the OP's bike is even older and more likely to have bad O-rings.
I used to drain the carbs when going out of town, come back in 6 months and my carbs would leak fuel for 2 or 3 days then be fine for the season. When I rebuilt the carbs this year I replaced ALL 0-RINGS and I have zero leaks.

[kingston73]

I've only ever had twins in the past, with inline 4 if I take the carbs apart and replace the orings will I need to resync the carbs?

[mollusc]

Yes.

You will also need JIS bits to separate the carbs.  There are no Philips screws anywhere on your bike, and using Philips bits on high-torque screws WILL strip the heads.

[Bob H]

...with inline 4 if I take the carbs apart and replace the orings will I need to resync the carbs?

First step is to try and pin down where the fuel is coming from - before disassemble anything.

Kind of like an oil leak, sometimes you have to clean the area like an operating room and watch for that first spec of fluid coming out.

[Larry Fine]

Some talcum powder can help with that.

[Pete in PA]

Those O-rings will probably come out in pieces.

Mandatory to split the carbs and replace them unless you know you recently did it.

[kingston73]

I haven't started taking the carbs off yet but my coworker just gave me another set he had laying around.  He had bought them and rebuilt them but never installed them. They are off an 84 nighthawk 650 and look mostly similar except for one difference, I'll let the pictures talk but I'm wondering what the connecting rubber tubes between the carbs are for?  I see divots in my original set, why did honda do that?

Also the slides are different colors, does that mean different materials or just dirty vs clean?

https://imgur.com/yYkgVpt

[Bob H]

... I'm wondering what the connecting rubber tubes between the carbs are for?

I don't see that in your photo.

Also the slides are different colors, does that mean different materials or just dirty vs clean?

I have a different model 1993, but my slides are your dark color example and mine were not "dirty".
Should be OK to use, as far as the slides.

[kingston73]

Sorry, meant to link the whole album
https://imgur.com/gallery/FoTiWxI