Really weird fuse blowing/smoke problem

[isaac]

I've had my 82 GS 750 for a month now, and so far it's done this twice. The first time was a week ago: I was riding the bike like normal, and I get to a stoplight and it just dies. The lights on the dash don't work, the starter won't engage, and the second fuse from the bottom is blown. I swap the bottom fuse into its place, and the bike fires up and runs fine, so I buy 5 fuses at the hardware store and head home.

I have no idea what the fuses are because the side cover isn't original on this bike. I'd really appreciate it if somebody could list me what the fuses are supposed to do and what their amp ratings are. Thanks for that.

Anyway, so I'm riding today and it does it again, only this time it keeps doing it with each successive fuse install, and the bike is running weird. Theres smoke coming out of the right side of the instrument cluster too, presumably from the oil temp guage. That occurs even with the fuse blown.

It won't hold a fuse now. It blows them in that one slot within seconds of starting the bike, though never instantly. Once the bike is started, even if the fuse blows, it will continue to run, but all the lights are off and it runs like crap. It can be ridden, but only really in first gear, and it won't top 10mph, and backfires pretty frequently.

A very weird quirk: If I hold the starter button down, it runs much better and can go 20mph. OF course that probably is the starter helping out, but I could swear the engine smooths out. That only happens if I hold down the starter button.

I got it home since it did this half a mile from the house, but that sort of sucked pretty badly. I'm pulling it apart to take a looksie at everything, but don't know where to look on account of not having a fuse chart.

 

[Jethro]

Sounds like a short of some kind.

Anyone with a 82 750 can our brother here out by having a look at thier fuse box cover?

 

[Jethro]

Just checked out my 81 1100 which is darn simaler to your 82 750- 2nd fuse up from bottom is the main fuse.

That would make sense. Unfortunately, I assume the short could be anywhere.

Isaac to Earl, come in Earl...

Earl will know where to start.

 

[Anonymous]

Where theres smoke theres a short, 8O Id check first where the smoke was coming from & trace the burnt wires to the shorted out point

 

[earlfor]

Uhhh Jethro, 1100's have five fuses and late model 750's have four. Also, the order is half reversed. And........................as it turns out,
late, late model 7f50's apparently have five.

Earl

Just checked out my 81 1100 which is darn simaler to your 82 750- 2nd fuse up from bottom is the main fuse.

 

[earlfor]

Isaac, how may slots for fuses are there in your fuse block?
I want to be sure it hasnt been swapped for something else before I start telling you do this and that.

Earl

 

[isaac]

Thanks for the help so far, guys.

This bike seems to have the traditional 5 fuse setup. So what are these fuses supposed to do? Since the one that keeps blowing is the main, I guess it's a lot of stuff.

I got the instrument cluster open and can't get any indication from looking at the cluster that there's anything wrong. I'm not seeing anything melted. I'll start checking deeper though.

One more thing: All the other lights function, but the neutral light suddenly doesn't.

 

[earlfor]

Ahhhh! 1977 to 1978 had one fuse, 79 to 81 had four. I never had an 82 or newer 750. Obviously then, they went to five that year.

OK, standard order. (the fuse block mounting tabs are symmetrical so it can be mounted right side up or upside down.) It is right side up if the fuse block wiring exits the bottom of the fuseblock.
from the bottom, moving up. 1. Power source 15 amp. There is a red wire coming from your fuse box and connected to the battery positive. This supplies power to the fuse block. Everything in the fuseblock is powered by this supply line.

2. Main 15 amp
3. ignition 10 amp
4. signal 10 amp
5. headlight. 10 amp

If you are blowing the 2nd up from the bottom, you are blowing the main.
The fault then could be in 2, 3, 4, or 5.

You have a short, so we know anything you put in #2 is going to blow.
Might as well use the lowest rated fuses you have. Dont use high rated fuses, we dont want to burn wires before the fuse lets go.

You have smoke, so you have already burned something up. Besides finding the fault, you will need to do an electrical repair.

Remove fuse numbers 2,3,4 and 5. Turn on the ignition switch. 1. should not blow.

Install fuse #2. You now have 1 and 2 installed. Turn switch on. If it is a wiring harness fault, the fuse will blow.
If it does not, leaving the ignition switch on, insert the #3 fuse, if it doesnt blow, insert #4, if ok, then #5.

Let me know at what point the fuse blows. Then we can do individual circuits.

Earl

Thanks for the help so far, guys.

This bike seems to have the traditional 5 fuse setup. So what are these fuses supposed to do? Since the one that keeps blowing is the main, I guess it's a lot of stuff.

I got the instrument cluster open and can't get any indication from looking at the cluster that there's anything wrong. I'm not seeing anything melted. I'll start checking deeper though.

One more thing: All the other lights function, but the neutral light suddenly doesn't.

 

[Jethro]

Uhhh Jethro, 1100's have five fuses and late model 750's have four.

This bike seems to have the traditional 5 fuse setup.

HA! I was right and Earl was wrong! The earth is gonna shift off it's axis!

Pllllupppptttt!! (big raspberry in Earls' general direction)

Course, I have no idea how to troubleshoot this problem and I'm sure you do, Earl.

 

[earlfor]

LMAO Jethro. eh eh Well, let me put it this way. I may not get the troubleshooting right, but I can narrow it down to a minimal number of wrongs.

Earl

HA! I was right and Earl was wrong! The earth is gonna shift off it's axis!

Pllllupppptttt!! (big raspberry in Earls' general direction)

Course, I have no idea how to troubleshoot this problem and I'm sure you do, Earl.

 

[ZacharyB]

I will just throw this out there...

My 78 750 was blowing its fuse after I installed a new rectifier/regulator. It was when I came to a stop, too. I figured the brake light circuits were doing it because of the stopping. I couldn't find anything. Maybe my old, corroded-looking ground wire was insufficient for the new big voltage my stator was putting out? That turned out to be it.

 

[Poot]

sounds like you bought the wrong amperage fuse, and that there is also a short.

take one thing at a time though. earl listed the amp. ratings. I also had a very similar problem, which was not the short but the wrong fuse : {|~

 

[isaac]

Thanks a lot for the extra help, guys. We're getting closer now.

I think I've narrowed down the problem. If I attach the orange wire to the oil temp sensor, the fuse blows. No big deal - I'll just leave that guage unpowered. It never worked right anyway.

I also replaced the 4amp fuses that had been in there with higher amperage ones. The main fuse doesn't seem to want to blow anymore, at least not on cranking.

Then when I'm checking the main connections I notice some stuff. The main red power connection going into that little metal tube shaped box to the left of the fuse panel (what is that?) is pretty corroded.

I busted out the drill with wire brush on the end and cleaned that off, then took a look at the main ground. Lo and behold the metal underneath it was still painted. I stripped that off, cleaned that, then put it back together.

Here's the problem: While messing with the main power connector on top of the tube/box next to the fuse panel I accidentally made sparks fly from the connectors on top, seemingly from grounding them out.

Now the bike won't start. Did I do something to that canister that would cause the bike to not run? What can I do to fix it? Thanks much for the help.

 

[focus frenzy]

check your main fuse again, that "thing" is the starter solinoid.
depending on how you shorted it, you may have blown the fuse.

 

[isaac]

Leon, thanks for the help there. Yeah I guess the solenoid's fine. It cranks and all, but won't kick, won't sputter, won't start. The main fuse no longer blows.

Needless to say I'm now thinking this is a spark issue.

What could have gone wrong between when I shut off the bike (while it was still running crappy, but running) and today that could keep it from sparking? Is the orange wire I pulled from the oil temp guage somehow part of an elaborate setup that when disconnected makes the ignition worthless? Could I have somehow blown both coils or the ignition? Thanks for the more help.

One more thing: Whats that plasic, tubular, see through relay looking thing under the gas tank that connects to the starter solenoid? It doesn't seem to be clicking at all when I go to start it, but the bike still cranks.

 

[nabrams]

A few years back I installed a faulty regulator/rectifier on my bike. I started the bike and things started smoking and instrument bulbs blew out until finally the main fuse blew, preventing further damage.
You may have had a faulty R/R that was failing slowly enough to cause some wire melting before blowing the fuse. The repeated attempts may have caused some more melting.
Anyway, at this point I suggest getting a good multimeter and testing the main electrical components (stator, R/R, coils, etc.) to verify that they're all up to spec (see stator papers in the garage section of this site). You will be a bit intimidated at first but once you find the problem you'll say "Got ya!" and you'll feel better about not having to play guessing games anymore. When I found my R/R putting out 18 volts, that sure clarified the problem.
If all of that checks out OK then check to verify that all plugs are firing (see other posts on how to do this). I'd also try to pinpoint exactly which wires have melted so far, if I were you. It would be a shame to get everything else straightened out and then have short circuits that will mess you up again.

 

[isaac]

The list:

I've taken a good look around at all the wiring and nothing's melting.

The green neutral light still won't come on, but that's the only bulb blown (or somehow not being triggered).

It's measuring 12v at the coils and the kill switch.

The previously disabled neutral safety switch and kickstand switch had never been an issue before.

It cranks just fine, but won't fire.

Fuel flow is fine (hence my suspicions of spark problems)

I've read stuff about ignitors and signal generators going bad and was wondering if those could have anything to do with this.

Reminders: Bike blew the main fuse last week and died, no dash lights, starter wouldn't come on.

Replaced fuse and the bike fired right up and worked fine for a week.

It did the same thing again this time, blowing the fuse five times on the way home, but continuing to run with the main fuse blown if I held the throttle. It actually got me home like this (main fuse blown but bike still running barely) in first gear at 10mph.

Now after seemingly fixing the blown fuse shorting out problem due to the oil temp sensor it won't start at all. Replacing the fuses and cleaning fuse and main wire connections has done nothing.

What could I have done wrong here? thanks.

 

[nabrams]

Did you actually check for spark (and see a blue/white spark on all plugs)?
Without that sanity check you're still just guessing as to whether the whole igniter/coil/plug/signal-generator combination is actually functioning or not. If you get even a weak spark you bike should at least sputter (catch a little) on a startup attempt. You haven't played with the carbs or air filter so it is almost certainly not either of those.

 

[isaac]

It's not sparking at all on any of the 4 cylinders. Something's keeping that from happening.

I'm thinking and hoping it's some simple circuit between turning on the key and the bike lighting up that's keeping the spark from happening.

I'm getting 12 volts to the orange wire going into the back of each coil with the key on. The yellow/black wire going into the front of the right coil is getting about a volt less. The white wire going into the front of the left coil is only getting a little over a volt. I'm not sure what that means, but I'm hoping that's a major clue. Help?

 

[isaac]

New stuff: The bike blew the bulb for the neutral light. I don't know if this means it's lost the regulator and is going to 18v or whatever, but it seems to me that it would have blown them all if it did that.

I checked the resistance on the primary terminals on the coils. One one of them it's at 3.8 ohms and the other is 4.3 ohms. Those seem to be within acceptable range.

I've seen things about checking the module and if it's bad possibly opening it up and resoldering it. How do I check it? Is it a resistance between the terminals thing? What are the values? Thanks for the help.