hot coils

Hey gents,have a few issues here.1984 gpz 1100.all stock electrical, except dyna ignition, new stator,reg-rect,and battery,I have lower voltage readings from fuse box to ignition..12.00 down to 11.47.if i take a reading from the coils i get 10.87+-. Also had coils from 1989 zx7 installed.but they became extremely hot. with just the key turned.while i was checking the voltage. Any ideas of whats going on?

Can you check the primary(small wires) side of the coils when they are out of the circuit(disconnected)? They might read 2.0-3.0 ohms using a multimeter.

My understanding is the lower ohm coils may get hotter than a higher reading set would(or is it the other way?).

Where the ignition coils are mounted is not the best working conditions as air flow is restricted until the bike is moving and vibration varies in frequency and amplitude.

If it's a Dyna S or Dyna III, the coils get powered up almost continuously. That is one drawback of those ignitions. Also, there is a 3-ohm minimum on those ignitions. If your coils are lower than 3-ohms, you may be stressing the ignition system beyond what it was designed for.

the readings were 3.5 and 3.7 at the primaries.for the zx7 coils. and 3.0 and 3.1 for the stock coils

i ran the stock coils,but was having voltage trouble.then i switched to the zx7 coils. which were getting hot.

MFolks wrote:

My understanding is the lower ohm coils may get hotter than a higher reading set would(or is it the other way?).

Lower Ohm coils get hotter if they are getting the same voltage across them for the same amount of time (duty cycle). The Kawi ignitions with points (which puts the full 12V or 14V across the coils) were four Ohms. The lower impedance coils (like 3 Ohms) are for use with electronic ignitions where the full 12V does not appear across the coil because some is lost across the solid state switch element. Also, they may have a lower duty cycle which means less average power dissipation in the coil.