Wierd arcing to frame?

Tonight, working on my M2, I was making some adjustments to the carb mixture screws. I had a long screwdriver that I was threading down through the center of the frame from the top to reach the #2 carb air screw.

Suddenly I noticed that where the shaft of the screwdriver came in contact with the frame tube, there was a constant electrical arcing between the screwdriver and the frame. The engine was running, and I assume the juice was somehow coming from the coils. Is this normal? If not, what could be wrong?

Why would there be current flow between the carbs and the frame? They are isolated (electrically) from the frame, except through the throttle cable, right?

Is this something to worry about?

Thanks.

Any ideas?

No electro guy here but sounds like your creating a "ground" with the screw driver?. Check all connections and try again.

There are many things that can cause that. For this problem, we can divide the bike into two distict electrical systems. The high-tension side and the primary side.

To determine if it's a primary side (or battery-side) problem, measure the voltage from the battery's negative terminal to the motor (with bike running). It should be preferably less than .5v. Measure the voltage from the battery to the frame. It should also be preferably less than .5v. And in your case measure the voltage to the carbs. It should also be less than .5v.
Then do the same measurements, but with the meter set to AC volts. The readings should all be near 0v.
If any of those fails, then you have a bad ground connection somewhere.

Now for the high-tension side. With the bike off and the coils disconnected (and sparkplugs disconnected), measure the resistance from the metal core (the mounting bar) of the coils to the high-tension output of the coils. If the wires are easily removable, then remove them to do the reading. Otherwise, measure to the end of the sparkplug wire where it connects to the sparkplug. If there is any continuity, the coil has an internal short. Do the same measurement from the primary contacts to the high-tension side. If there is any continuity, the coil has an internal short. Lastly, check from the primary contacts to the coils core. (Remember, these are all to be done with all of the wires disconnected from the coils and/or sparkplugs.)

The problem with these coil-tests is that the short may only occur while there is several thousand volts on it. That means the resistance test won't show the problem. In order to truly rule out the coils, you have to un-mount the coils (then reconnect the wires)and get the bike to run while the coils are floating and not touching the frame. Then check for your spark-to-screwdriver test.

Oh, and obviously, you need to fix this. Arcs and gasoline don't play well.

Post edited by: loudhvx, at: 2008/01/04 15:33

Thanks. I'll do those tests tonight.

Loudhvx,

I performed all the tests you suggested except for the last one.

What I found is that on my 2/3 coil, I have no continuity/resistance across the secondary winding (plug wires).

Seems weird to me as the bike seems to run okay. Just to make sure this wasn't normal, I checked my 1/4 coil, and had about 14k ohms on it.

I did a little further checking and discovered that I had the polarity reversed on the primary leads on my 2/3 coil. I'm guessing that would explain the arcing I saw. And I'm guessing I may have fried my coil, since I now have no secondary resistance. Damn.

Okay, I did some more tests.

I put the coils back on, this time making sure I got the primary polarity correct.

I checked the plugs for spark, and got good spark on all four.

I then tried my screwdriver-carb-frame test again, and STILL saw arcing between the screwdriver and the frame tube.

I then tested again for resistance between my 2/3 plug wires. THIS time, I got 14K ohms. :blink:

Maybe because it was warmed up???? Maybe the coil is on its way out, but not quite dead yet?

Here's something weird. I tested for continuity between the carb and the frame and got zero, zip, nada.

So why would I be getting arcing going on when I bridge a screwdriver between the frame and the carbs? Any chance that it is static discharge?

Loudhvx--any ideas? Anyone else?

Thx.

the carbs are rubber mounted, with the only path to ground going through the throttle cables. i would not expect any or little continuity through them. do a voltage drop between the engine case and neg. bat terminal while running should be real low like .02 or so. i would guess somewhere you have some grounds going bad and you have some stray voltage floating around

Matt, I measured .03 volts. Does that possibly eliminate the chance that it is a bad ground?

Note, the arcing only happens while the engine is running, and only when I bridge between the carbs and the frame.

Possible leakage of current through plug wire insulation to frame.

Could try the water spray test over plug wires in dark garage while engine running. Might see sparks arcing from plug wire to engine or frame.

Forgot to mention -- am thinking the coil primary windings are not polarity sensitive (so it doesn't matter which primary terminal receives battery voltage). And the other primary coil terminal connects to wire from the ignition trigger.

With the green Dyna coils, the primary terminal screw heads are located very close to the spacers on the mounting bolts. To insulate the screw heads from the mounting bolt spacers, I use a couple of small plastic tie wraps snugly around each spacer to serve as insulation from the coil terminal.