loud bang, bright flash, then the stop lamp came on...

I have an '81 KZ550 that I've been riding for about 10 months now. This evening I had my first real problem with the bike.

I was riding home on the freeway the tach was at 6000 RPM and had been around there for about 20-30 minutes, all of a sudden there was a lound bang under me accompanied by a bright flash. I went shit that was a big backfire (I think I was rolling of the throttle at the time) but then I looked at the tach and the stop lamp is lit, shit. So I pull to the side of the road, try to look over the bike in the dark (I don't really see much of anything) I try to start the bike again after it sat a few minutes and it fired up just like normal, no lights nothing, I run it down the shoulder of the highway, nothing seems any different than normal. All I can notice is the slight ticking from my valve train that I have had for a while (only noticible when at idle).

So I guess my first question is what does the stop lamp on my bike actually indicate (ie what is it hooked to) I don't have a manual to tell me these things. Also any ideas where to look first when it gets light out.

Sounds like you've got a short in the wiring somewhere.

First thing you're going to want to do before even starting the bike again is to check ALL of the wiring, connectors and fuse box for problems.
The wiring underneath the fuel tank and inside/behind the headlight are the usual areas shorts appear, since there are plenty of spots where the wires can be pinched or rubbed through.
Other things to check are the ignition switch and handlebar controls wiring since they're exposed to the elements more, and also prone to becoming pinched when the handlebars are turned.

on my 78 1000, the stop lamp is activated by the brake light switches. so it's telling you when you hit the brake (as if you need to know)

dunno if yours is the same though

On some bikes the stop lamp is on until
the motor is running.Are you running pods
or velocity stacks? I would definetly give
the bike a good look over,timing,valves,
plugs,wireing,cam chain tension tec..

Not to be a killjoy here guys, but worrying about if the stop light in the tach is functioning or not is addressing the symptoms and not the cause.

IMHO he needs to find out what caused the..."lound bang under me accompanied by a bright flash"...which killed all of the other lights.
Now that I've re-read his initial description, I'm more inclined to think that his seat pan might be hitting the battery posts and causing the problem he has.

I guess we won't know until/if he chimes back in after checking everything.

Ok, I think I have narrowed down some of the symptoms. I think the bang and flash was in fact a big backfire caused by the ignition system cutting in and out. Yesterday I checked all of the fuses and pulled the tank off and the wires there all look fine at least visibly. I rode it briefly yesterday and experienced random losses of power (ie the engine sputtering and then coming back) this was almost always followed by a backfire. So, what I'm thinking is that the ignition system is cutting in and out and the backfire occurs when the ignition cut back in and ignites all the fuel. Does this seem like a reasonable conclusion?

As for the stop lamp it seems to come on when the bike is trying to stall, and this is the first time I've ever seen it work (doesn't come on when I start the bike), so it may indicate a stall.

Here's what I'm reading: the "stop" light comes on when you're not hitting the brakes and possibly when the engine misfires. On my KZ650C1 the stop lamp only comes on when I hit the front or rear brake. The front brake light switch is attached at the brake line splitter between the forks, and the read brake light switch is on the frame above the rear of the brake pedal. If you bike is like mine, but if the "stop" light comes on when you're not hitting the brakes, then you either have a short that is sending power to the brake light circuit or one of the brake light switches is doing very weird things. If it's a short, it may be pulling power from other components (ignition, other lighting, etc.). I would check the brake light circuit VERY carefully tracing it from the stop light indicator light between the gages to the switches, rear brake light fixture, and any grounds. If you find the source of that problem you may find the others at the same spot. Ed

If your bike is like mine and if you are correct and the ignition is cutting out momentarily, then remember that the Coil wire has to go all the way up to the right switch gear's Kill switch and all the way back down to the Coils. Either check the Kill switch (watch out for flying springs and ball bearings when disassembling) or by pass it. See if the symptom disappears.

The flash and bang symptom may or may not be related... I would get the Coil voltage done first.

By the way, I think the WG Coil Re-powering Mod might be a good move since your tank will be coming of.

Best of success.

Well, it looks like I have a weekend full of playing with a multimeter on the bike. I was thinking about doing the WG coil mod while I was at it. Also its time to look at all those mechanical things I have been putting off for off season.

nosbearatu wrote:

the stop lamp is lit, shit. So I pull to the side of the road, try to look over the bike in the dark (I don't really see much of anything) I try to start the bike again after it sat a few minutes and it fired up just like normal, no lights nothing, I run it down the shoulder of the highway, nothing seems any different than normal.

Check your chassis ground,(battery to chassis) it's trying to ground it's self through anything, including lights.

Okay, so you have a light which never works unless your bike is screwing up. So that means you are taking a normally dead circuit and powering it off a normally live circuit. All you have to do is start at the ground of the stop lamp circuit and trace it back to the ignition switch/battery you should find some place where the wire contacts the ignition circuit be that at a raw wire, a connector, or (my bet) the ignition switch. The key to your sanity is to start at one end and follow it to the other end.

Your description suggests that your stop lamp is providing a shorter ground to the ign. and drawing power off that circuit. I'm with 650ed in that I think your problem will be found either in the light/guage cluster or the ign switch, but it's still more reliable to ALWAYS trace electrical problems systematically either from the power end or the ground end, never from the middle. Just how I was taught, and never fails me.

Don't know if this helps with the 550, but here's how the dash warning brake indicator light is supposed to work on the KZ900.

Per FSM: [KZ900]...is equipped with the brake lamp failure indicator lamp which indicates whether or not the brake lamp is functioning properly. Brake lamp failure may be due to a burned out bulb or to some other failure in the brake lamp circuit.

As I intrepret the FSM, it goes on to say that while riding along without brakes being applied, the indicator light should normally be off, but it will flash to indicate the brake light bulb is burned out (still without brakes being applied). So if you see the indicator light flashing while you are riding along without brakes being applied, it is warning that the brake light bulb will not burn when you do apply the brakes (eg., the brake light bulb filament is burned out). And when brakes are applied, the indicator light should be steady on regardless of brake light bulb condition.

Here's the test with engine off to determine whether the brake light failure indicator switch is functioning properly --

Turn ignition switch on (indicator lamp should stay off). Apply brakes (indicator light should turn on). With brake still applied, remove the tail light bulb (indicator light should stay lit). With tail light bulb still out of the socket, release the brake (indicator light should flash). These results indicate that the brake light failure indicator switch is functioning properly.

If your situation is blinks when not braking at all, could be simply a iburned out brake light filament in the taillight bulb.

However, (continuing to blink while holding steady pressure applying the brakes) could indicate a malfunction of the brake light failure indicator switch located under the tank (three wires, being yellow, black and green/white), pluged into a 3-wire connector (same colors) from the wiring harness.

Good Luck with the repairs.

Post edited by: Patton, at: 2007/08/25 12:10