I think theres a plastic coil box rebuild kit in my future.

[mbowen]

Today I awoke Clyde, my 1925 Express Wagon from an 8-month slumber. It started easily, though I did get a backfire as it was starting. It seemed to run fine for a few minutes then got rough and lost power.

I had just reinstalled the timer, so the first thing I did was check the wiring - all as it should be. I then started to check the timing and noticed the number 3 coil was firing continuously, regardless of crankshaft position. Checking the primary terminals for a stray ground revealed nothing. Swapping coils 3 and 4 caused no change - coil 3 continuously firing. Removal of the coil box for a closer inspection revealed what I believe to be the problem: carbon tracking from the #4 secondary to the #3 primary. I’m not sure how it happened, as it’s been stored in the same dry, heated (50F) hangar with Bonnie, my ‘24 Touring (that gets driven at least once most weeks), and also has wood coil box terminal panels. The only difference is that Clyde has been sitting since last August with an open coil box and no coils.

[Steve Jelf]

Yes, that could be your problem. But a continuously buzzing coil can also come from the top timer terminal touching the control rod, so check that while you're at it. Maybe you can guess how I know this.

[mbowen]

Thank you Steve, I’ll do a visual check, but my ohmmeter (on a 20-ohm setting) showed an open circuit from all primary terminals to ground.

[Jerry VanOoteghem]

Miles,

The carbon tracking wouldn't explain a continuously firing coil. Also, I think what looks like carbon tracks is just deposited lead that occurred when someone pulled the #4 coil out by sliding it sideways, rather than straight up.

It's good that your coils wires showed no continuity to ground. Did you check the #3 terminal on your timer for a continuous ground?

One last thing, your coilbox is missing the small support bar that goes from the box front wall to the wooden back. It sits between coils #2 & #3. This helps the support the box front wall, so it does not sag outward, allowing the coils to fall away from the contact springs. Again however, not your immediate problem.

[mbowen]

Thank you Jerry. I did the checks with the timer installed, so I’m pretty sure all the terminals are isolated. I did only check on the 20-ohm scale, so if there was a higher resistance path to ground I would have missed it. There is a horizontal track on the wood between the #3 and #4 primaries, but the outside of the wood is clean. I don’t see a path to ground, but strange things can happen at high voltages.

[Oldav8tor]

Lead is also a conductor. I don't know if a lead track across wood could cause a short or not. It might depend upon the voltage. Perhaps, like carbon tracks, they mostly come into play at high voltages. Regardless, a plastic coil box kit may solve your problem or simply prevent future ones.

[Wayne Sheldon]

Ohm meters vary, mine, I usually test for shorts on the ohm X 1000 or even a higher setting. Low settings can often miss active shorts.

I would suspect the timer still, or one of the contact posts around the timer. Even if, maybe especially if, the timer was recently cleaned. Seen it many times, and even done it myself. Wash or wipe the timer clean and some errant bits of metal debris settle into just the wrong place and result in a resistive short that can drive one crazy trying to find it. Or the timer rod sets in just different enough to touch where it hadn't before.

Carbon tracking in coils boxes is usually resistive enough that a common ohm meter will not read it (requires a "mega-ohm meter"!). Carbon tracking usually doesn't cause a coil to buzz continuously unless the wood is also wet (very wet!). Carbon tracking usually reaches a point (either wet or dry?) where the high resistance short becomes a lower resistance than the air gap in the spark plug causing it to misfire.

[mbowen]

Jerry and others were right; the issue wasn’t carbon tracking. The orientation of the #3 terminal on the timer was such that it contacted the cam gear cover. Evidently I had done my isolation checks with the timer off. I corrected the #3 terminal and it runs fine now, but I am going to get the plastic rebuild kit.

Another poster emailed and suggested that the terminal board is aftermarket and its terminal slots may not be cut correctly and not lining up accurately with the coil terminals, especially on #1. That would also explain why there’s no slot for the support bar across the center of the box.