Blowing the fuse!!!!

[rngdng]

After 12 years of perfect reliability, Blueboy has decided it's time to blow the main fuse. It's been a while guys and there are some things I've forgotten. For instance, the GT750 wiring diagram shows a black/white wire on the rectifer which does not exist on the LMAB bikes. My rectifier reads good.

I removed my custom ignition system and re-installed the condensers so the ignition is back in stock condition. When I turn the ignition switch on, the neutral light looks strong, but kick it over a couple of times and the light dims, and eventually the main fuse blows. So that tells me it's not my custom ignition; no change in symptoms with it removed, but something is dropping voltage and blowing the fuse.

Any ideas? I think maybe a shorted coil, but two weeks ago it ran fine, and now this crap......



Lane

[tz375]

Lane,

Try pulling the 6 pin connection at the coils and see if it still blows a fuse. If that stops it, it's probably a short in the ignition circuit somewhere. If it still blows open up the headlamp shell and look for a short

[rngdng]

I have the headlight opened right now, and can't SEE anything wrong. I have to get some fuses and start experimenting.

What I can't remember about the rectifier is how do I measure the other three diodes? In the schematic you would read three of them relative to the red wire and three of them relative to the black/white wire which I don't have. I'm sure three of the diodes are good....


Lane

[Craig380]

It could be an internal short in one of the coils, I had that intermittently on my 380 a while back. It would short after around 10 - 15 miles of running, and would stop the engine dead as if I'd hit the kill switch as it took pretty much all the juice from the battery. The neutral light wouldn't even glow when the short happened, it was a dead short. Flicking off the kill switch restored power to the lights etc.

30 minutes later, the coil would cool down and the bike would fire back up like nothing happened, but would short again after another 10 miles or so. It started literally one week to the next, no warning. Never blew the fuse, though.

[rngdng]

I had something like that with my 84 RZ350. It ran whenever it wanted. It was a ECU problem which was fixed in 85. Maddening.


Lane

[Coyote]

In my case it was the tail light on the 550 you saw when you were here.. You might disconnect the tail light and see if that helps. Never did actually find the short. Removed the assembly and remounted twice. The short finally went away when I replaced the bulb. That led me to believe the bulb itself was shorted. Of course in my case the fuse blew within a few seconds.

[rngdng]

I forgot about that, Chris. That was a weird one. I'll get it, I'm just glad to eliminate the electronic ignition system. Hopefully I can get into it next weekend. Coil seems most likely. I think I have others, but I'm not positive.



Lane

[jabcb]

Use something to insulate the point contacts so no current is going thru the points.
Then look for voltage drops.

Also check the wires behind & below the battery box.
Some time ago a forum member posted a pic of a wire in that area that had the insulation worn down to the point it could short out.

[Suzukidave]

My volt meter when set on Ohms has a beep setting so i set it on that and put it in place of the fuse with the battery disconnected . When the system goes to ground the ohm meter goes off .

[jeff g]

After 12 years of perfect reliability, Blueboy has decided it's time to blow the main fuse. It's been a while guys and there are some things I've forgotten. For instance, the GT750 wiring diagram shows a black/white wire on the rectifer which does not exist on the LMAB bikes. My rectifier reads good.

I removed my custom ignition system and re-installed the condensers so the ignition is back in stock condition. When I turn the ignition switch on, the neutral light looks strong, but kick it over a couple of times and the light dims, and eventually the main fuse blows. So that tells me it's not my custom ignition; no change in symptoms with it removed, but something is dropping voltage and blowing the fuse.

Any ideas? I think maybe a shorted coil, but two weeks ago it ran fine, and now this crap......



Lane

If that is the only change to the electrical system that you made before Blueboy started blowing fuses, I'd start by checking out the connection at the points. Besides the obvious of having the wires in the correct position on the points, make sure that the insulator in the points assy is not damaged. I've had them break/wear out/crud up and short to ground which could allow the coil to overheat and short out. If that is the problem, change the coil also as it's not long for this world anyway.

Jeff

[rngdng]

If that is the only change to the electrical system that you made before Blueboy started blowing fuses, I'd start by checking out the connection at the points. Besides the obvious of having the wires in the correct position on the points, make sure that the insulator in the points assy is not damaged. I've had them break/wear out/crud up and short to ground which could allow the coil to overheat and short out. If that is the problem, change the coil also as it's not long for this world anyway.

Jeff

Jeff, it started blowing fuses before I removed the ignition. It seems to be OK until I kick it over then the neutral light dims, and the fuse blows.


Lane

[tz375]

Lane,

Does it still do it with the coil 6 pin connector unplugged? If that fixes it, try a spare set of coils.

Another possibility is the orange lead to the regulator which can chafe against the frame or the electrical panel behind the right side cover.

[rngdng]

I haven't done any more yet. I'll post an update when I can get to it. Hopefully this weekend.

Thanks,
Lane

[rngdng]

OK, I found it. It seems that when I replaced my fork tubes last week, my steel brake line got too intimate with the hot wire on the horn! STUPID!!!! Once I insulated the crap out of everything and re-routed the brake line a bit, all seemed good again, no blowing fuses BUT it still wouldn't start. I kicked and kicked. Wet plugs.... but the spark was gone. I had it earlier...?!?!? I did change something in the headlight shell, though. I removed the connector for the starter button as I took the electric starter off years ago. Well, it seems that connector is important. I reconnected it and the old boy started right away.

I have to look at the schematic to understand why, but at least it's running again. I'll put my custom ignition back on tomorrow.


Lane

[Suzukidave]

All right .. Blue Boy rides again .