Main Fuse Keeps Blowing

[gaillarry]

Working on an 83 GS650 basket case that I just brought back to life. Did the usual carb cleaning, changed plugs, oil. etc. Bike starts and runs for about 20 seconds, then the main fuse blows. Obviously something is shorting out but where to start looking?

[liloaty]

This seems odd but try it with the tank off. I was having the same problems, pulled the tank and didn't blow the fuse. The tank was rubbing a loom of wires and had worn through like 3 or 4 of them.

[Steve]

Main fuse keep blowing.

Well that really sucks. :-\"


Well that didn't help you much did it? 8-[

Your fuse panel probably has 5 fuses, like my '82 650L. Remove the top fuse (headlight) and the second fuse (turn signals and brakes), then try again. If it happens again, try it without running the bike. You might also want to verify that the third fuse (ignition) is really a 10A fuse like it is supposed to be. Somebody might have substituted a 20A fuse, so the 15A main fuse blows, instead.

If the fuse keeps blowing even when the bike is not running, you are going to have to go over the entire harness inch by inch to look for abrasions that might be shorting to ground. It is also possible that the shorting is inside the harness where you can't see it, but you might see where the outside of the harness has been rubbing on the frame enough for two wires inside to be rubbed through and touching each other.

.

[posplayr]

Well you sound a little desperate

So I'll see if i can help before someone suggests you read the stator pages.8-[

I guess the first thing to do is get a schematic and make sure you understand how many circuits are on the circuit of the fuse circuit that is blowing. If you can remove circuits and still get the bike to blow then you are doing a combination of "process of elimination" and "divide and conquer" methods.

Figure out what is the minimum number of things to have on and still get the fuse to blow.

It might be useful to get an VOM with at least a 10 amp scale. 20 would be better as you will probably blow fuses in the VOM or the 15 amp main fuse first. Amp meter would go inline with the main fuse to do this. Note if this thing is shorting bad then using the amp meter may not be required just go get a whole bunch of fuses. If you had a 20-50 clamp on amp meter (I know why the hell would you have one of those ) then that would be ideal. IVOM on volts setting will also certainly give a clue of voltage drop .


Things to try.
1.) How much does the current pull from the battery just sitting there. (gives you an idea of how much drain there is with every thing supposedly off). Simple test remove the negative cable and tap it to the negative terminal and see if it sparks. If it does this with the bike just sitting then you have a more serious short. Basically with all circuits off and the bike off there should be little if any little sparking when you do this. In a darkened garage it will look like little cracking sparks (negative to negative ) I DONT MEAN NEGATIVE TO POSITIVE that you might not even be able to see in daylight.

2.) Turn on the key alone (ignition current to the coils) If this doesn't blow anything then move on. You an retry the test above with the ignition on to see how much 3 amps will sparkle. See if anything blows.

3.) Turn on the lights, blinkers and turn signal or anything else to see if they blow. Hopefully you have success and nothing here blows else chase down those circuits.

4.) If all that works and doesn't blow the fuse you are getting closer to the charging system. And it might be time to try and rule it out. Remove the three wires coming from the stator to the R/R. See if you can make the fuse blow including starting the bike. If it still blows , disconnect the R/R completely. If it still blows you have a short somewhere.

I if you get rid of it it is likely in the charging system and it would be best to start swapping out parts of then go look at the Stator Pages. The first couple of tests on output voltage should tell you if you have voltages in the proper range or what is bad.

Try some of the above and report back, with more info others or I can maybe provide further guidance.

Posplayr

[gaillarry]

I'm not using a gas tank, just a portable fuel supply (old lawnmower tank).

The main fuse calls for 15A (marked on the fuse box) but I'm using 20A fuse (thats all I have handy).

I'll try the idea of removing the other fuses to narrow down the problem.

[gaillarry]

Started removing fuses and it's the "power source" fuse, the last one on the panel. I removed the fuse and bike runs great. I would guess the power source is for an external hookup such as lights. etc??

[gaillarry]

I do have a clamp on Amp meter but no idea on how to use it.

[Steve]

If it's the last one (power source), it only powers the terminals on the end of the fuse panel. Do you have anything connected to those screws? One of the screws will be a "hot" wire coming from the fuse, the other is a ground. If you have nothing connected to them, look on the back side of the fuse panel to see if there is something there that might be touching the back side of the fuse or the screw terminals. If you do have something connected to those screws, that might be what the problems is.

Let us know.

.

[Steve]

I do have a clamp on Amp meter but no idea on how to use it.

Are you lucky enough to have a DC clamp-on meter? Most clamp-on meters are AC only.

If it is a DC meter, using it is rather simple. Simply get enough room around the wire that you want to check so that you can put the jaws of the meter around just that one wire. Make sure the meter is turned on to the appropriate scale and read the display.

Actually, using an AC meter works the same way, but they will not work with the DC in an automotive or motorcycle application. The only place you could use an AC clamp-on ammeter would be on the individual wires between the stator and the r/r.

.

[posplayr]

Reasonable Clamp-on DC probe

I have the A622, and it can be very handy for field work. But ouch, that price is pretty hefty; I thought I probably only paid like $350 for it.

http://www.testequity.com/products/1241/

My Tektronix Oscope also scales the display output into amps so you can read it out directly.

http://www.atecorp.com/equipment/tek/THS730.htm

More pricey

I pulled this stuff out (of storage) to diagnosis and record some of the GS charging waveforms, but after diving into the GS750 charging lost track and am up to my ears in GS1100ED.


Posplayr

[gaillarry]

I checked the fuse panel and all looks good but I'm back to square one. The original problem is back.

Even with the fuse removed from the power source, the bike will start and run, then the main fuse will blow. I don't think its the fuse panel.

I'll start checking all the connections for corrision and give them a shot of WD40. Hopefully I'll find something.

* my clamp on meter is AC

[justmount1]

sounds to me like u might have a charging problem try testing out your r/r and stator

[posplayr]

Another alternative to the clamp on

Right now it seems that all your circuits are within the limits of their respective fuses limits but the total exceeds the main. You need to better determine current . It sound like you don't have a dead short but is high enough to exceed the fuse rating. This could easily be the charging system as most everything else is a light/coil that has a fixed resistance.

Since you don't have the clamp on (or a simple automotive amp meter), You need to go back through and figure out which circuits cause a jump in the current requirement.

So to start over you might go and get smaller fuses and start putting them one at a time into the fuse box to see how low you can set them. That will at least put an upper bound on the current draw. See which one blows first as you turn things on. See if the current seems unusual compared to what is on the circuit.

Start with 5 amps and make sure everything will run off of that. Obviously if you put a 1 amp fuse in and turn on the head lamp the fuse will blow so use some logic in your process.

And as suggested before, at some point if you can rule enough things out it is worth disconnecting the stator and R/R to see if that has an effect on the current draw. Do the easy stuff first ;"divide and conquer".

Posplayr

[posplayr]

OK another idea

So you dont have a DC clamp on meter, then the second best thing is to use you inexpensive VOM to measure the current in each Fuse leg.

We already know that the main 15 amp fuse is blowing but you should still be able to use a 10 amp VOM on any one of the fuse legs. Remove the fuse in the leg to be tested. Carefully Aligator clip your amp meter across the fuse holder (your amp meter is now is series with the fused circuit. Measure the current directly and have some spare meter fuses as you could exceed the probable 10 amp rating of your meter.

Don't do this if your meter is only rated for 300 mamps.

Posplayr

[gaillarry]

After all this discussion about the stator and r/r I disconnected the stator and HAPPY DAYS, the bike runs, no blown fuses.

Not happy it needs a stator but the problem has been solved. I've had good luck with RMStators so more $$$ from my stash.

Thanks for all the input.