Ignition coil out of spec

[kryptek49]

Hi,

I own a 1992 Suzuki GS500E, and live in the UK

The bike is currently only firing on one cylinder.  The problem appeared to be the ignition coil so I swapped it with one off my Dad's GS.  This appeared to fix the problem.

When you take the bike out though, you get about 200 metres up the road and the cylinder stops firing again.

I've looked in the Haynes manual and the primary winding resistance of the ignition coil should be 3.0 to 6.0 ohms.

The cylinder that works fine is at about 5.5 ohms, the second coil is at 17.0 ohms, the third at 16.5 ohms.

I've just gone to a local seller on ebay that was selling 2 ignition coils, I tested with a multimeter before purchasing and both were at about 18 ohms.

That means I've tried 5 ignition coils and only 1 was in spec.

So does this mean I've got extremely unlucky, its a common fault, or that a resistance of around 17 ohms is fine and the problem is elsewhere?

Any help would be greatly appreciated, thanks in advance

[mr72]

Resistance of enameled copper wire in a coil does not grow with age. Usually a "bad" coil will be short due to failed insulation (that enamel wearing through) or (more likely) open circuit due to a physical break in the wire within the coil. A resistance measuring in the teens is probably fine.

However, if it works when cold and fails when hot, that's a very typical behavior of a broken coil. Typically the wire has a hairline crack that makes contact when cold (contracting) and when it heats up it expands sufficiently to widen the gap between broken ends of the wire wherever they are and create a temporary open circuit. Then by the time the unsuspecting home mechanic gets the bike parked and unhooks the coil and gets a meter on it, it will again have cooled enough to restore continuity and you wind up baffled as to what's broken. Sounds like your "200 meters down the road" issue to me.