Ballast resistor

[bufallobiff]

1979 SF model had no spark...bypassing the ballast resistor gave us spark. As I understand it, the resistor is in the circuit only after the engine starts. Does this seem right? Our spare resistor reds the same resistance as the one in question. The schematic shows some diodes in that circuit as well. Are they built into the resistor ?

[jetmechmarty]

The resistor keeps you from burning up the coils. Install 3.0 ohm coils and bypass the resistor. The resistor is required for the stock 1.5 ohm coils.

There is no diode that I'm aware of in the resistor. There is a diode in the regulator circuit. It's in the wiring harness, under the fuel tank.

Test the resistor with an ohm meter. Is it open? If so, replace it.

[crazy steve]

The ballast resistor is always in the circuit, it's just bypassed while the start circuit is engaged. I assume you're looking at the ignition circuit when you say there's diodes, these are internal in the ignition box; if you're getting spark at all, they're good.

I would suspect either a poor connection in the circuit to the coils, or marginal coils. Check the coils for proper ohms on both the primary and secondary sides. Primary side should be 1.5 ohms if you still have OEM '78-80 coils and using the ballast resistor. The secondary should read 25K ohms with the spark plug boots installed, 15K ohms with them removed. You're allowed about 10% +/- on both measurements, high/low readings on either side will affect spark output.

And the only diode in the harness is between the alternator winding and the headlight relay on the '80-81 bikes. The earlier bikes don't have it.

[bufallobiff]

I appreciate your responses. I'm familiar with a ballast resistor as normally applied. Some automotive applications use a resistive wire to accomplish the same thing. Back in the days of points and condensors it was used to protect the coil from getting too hot if, by chance, you happened to leave the ignition in the ON position with the engine off and the points happen to be closed. In this instance, as I understand it, full voltage is available at the start and dropped when the engine is started as determined by the CDI box I assumine. My question was why did jumping out the ballast resistor restore the spark. It wasn't open. It had the same resistance as our spare and....the engine had been running with the resistor in place days before......

[bufallobiff]

I appreciate your responses. I'm familiar with a ballast resistor as normally applied. Some automotive applications use a resistive wire to accomplish the same thing. Back in the days of points and condensors it was used to protect the coil from getting too hot if, by chance, you happened to leave the ignition in the ON position with the engine off and the points happen to be closed. In this instance, as I understand it, full voltage is available at the start and dropped when the engine is started as determined by the CDI box I assumine. My question was why did jumping out the ballast resistor restore the spark. It wasn't open. It had the same resistance as our spare and....the engine had been running with the resistor in place days before......btw, our schematic shows 2 diodes in the proximity of that resistor

[crazy steve]

...btw, our schematic shows 2 diodes in the proximity of that resistor

If you're looking at a factory diagram, those are the representation of the plug-in bullet connectors. There are no diodes in the harness....

[bufallobiff]

Ahhh that's why they go in opposite directions,,, thanks