What is this thing behind my ignition coil

[joseph548694]

Howdy,

Can anyone help me with what the rectangular things behind my coils? They have wires coming out of them and are made of chalky material that can flake. I am guessing they are the some kind of resistor, but they look different than the diagram in the parts manual (I am guessing #18), and I also am not familiar with resistors being made out of this kind of material, whatever it is. In the parts manual it only looks like there is one. Have I correctly identify what they are, and if so are they an aftermarket product?

Thanks in advance, this forum has been a great resource for a novice like me and I appreciate y'all.

[DenverWinger]

Yup, that's the ballast resistor.

[Rambozo]

Yes you have two in your photo. Sometimes they are made and sold as one part, sometimes two. They are almost always made of ceramic like that. The one in the front is broken, not a huge deal as the active part is the coil of wire inside, but you might want to replace it before you have problems.

[WingAdmin]

Resistors made to handle higher current are typically encapsulated like that. They have a thin wire inside that limits the current due to its resistance, but any time you limit current, you absorb energy - which gets emitted as heat.

If they just had a thin wire, it would quickly get white hot and melt. So they encapsulate the thin wire in something that conducts heat, and that has a decent thermal mass. So the encapsulating material becomes a big heat sink, as it has far more surface area than just the tiny wire. It sucks the heat away from the wire, so the wire doesn't melt.

Some power resistors put the encapsulated portion inside an aluminum housing with fins on it, to further expand the surface area and make it even more capable of dissipating heat, increasing its power handling capabilities.

Power resistor

[joseph548694]

OP. So, according to the manual there is only one resistor attached to the coil, for some reason I have two. One is attached to the coil as per the manual, and the other one is free floating, hanging out right in front of my air filter intake. I pushed on it a little while the bike was running and it produced sparks and the engine died. There was a lot of questionable things done to this bike before, and I want to get it right, so my inclination is to remove the extra resistor. Is there any reason that someone may have installed an extra one?

[Rambozo]

All depends on how they are wired up and what the values are. It's possible that someone changed it from a single resistor for both coils to one for each coil. Compare it to the factory wiring and measure the value of the resistors. Then you can put it back to stock. Also do you have points or has it been converted to electronic ignition?
Are they even both hooked up? Because it's not so easy to get to the mounting bolts, I could see some hack mechanic finding a bad resistor, wiring up the new one, but not swapping out the old one. Just letting it dangle by the wires, or maybe a long lost zip tie was on it.