one Black coil, one Grey coil?

[Guest]

I've got a 81 gs550L. I noticed when i had the tank off that someone has spliced a grey coil in while the other that appears to be factory is black. i have not tried to start the bike yet. i've been going over it because it has sat for god only knows how many years. The grey coils were for points ignitions werent they?

[tom203]

Don't live in suspense, measure the ohms on each and compare. Best to remove spark plug caps. Check primary and secondary ohms.

[Griffin]

Some GS coils were black, some were gray, some were cream colored. They all work the same.

Measure the primary and secondary resistances. If you get 3 - 4 ohms on the primary and 25K - 35K ohms on the secondary, don't worry about them not looking the same, they'll work fine.

[shinzon1]

i'l check it out this weekend. thanks! never thought to check the ohms.

[Crankthat]

Probably just a replacement coil.
Always good to check though.

[Joe Garfield]

There are resistors in the plug caps - if you look inside you'll see a slot for a screwdriver. Inside is a ~5 kOhm resistor. I am just learning about this as I am sorting problems with my ignition coils. I could not get a reading across the secondary coil (spark plug side) due to a bad resistor. I removed the cap and got a low reading across the coil, so something is going on inside causing a short.

High resistance is associated with the internal windings - many windings are used to significantly amplify the 12v input voltage, hence the reading of ~30,00+ Ohms (with caps installed). So a reduced resistance across the secondary coils is a sign of degradation. At the same time, the resistors/caps will lose conductivity as they corrode so resistance will go UP across the cap. This means that a shorted coil can be masked by a corroding plug cap, which is part of what was going on with one of my coils.

The plug caps are actually threaded onto the spark plug wires, if you need to remove them for anything. Here is a pic of what is actually inside. The threaded piece is the plug contact. The white cylinder is the resistor (this resistor measured OK, the bad ones were black). The spring has some corrosion on it which was acting as an electrical insulator. I could not read a resistance across it. So even though the resistor was good the plug cap was not functioning properly. If you look at the narrow end of the plug cap, you can just see the brass or copper 'tip' which is threaded. That end threads into the spark plug wire.

This plug cap is serviceable since the resistor is measuring OK. Personally I would not use the spring - it could be cleaned off, and the loss in conductivity may or may not be noticeable. A new cap is about $3.50 so it does not seem worth the effort to restore it at this time, however the parts have been saved/donated for if the need arises.

[Don Williams]

I replaced the wires on my 1100gs with dyna solid core, so do I need resistor plugs?

[tom203]

Aren't you still using resistor style plug caps?

[Don Williams]

I don't believe so, these caps do not look like the stock or ngk caps, the're kind of flexible feeling.

[tom203]

I don't believe so, these caps do not look like the stock or ngk caps, the're kind of flexible feeling.

Well, I'm curious. Measure ohms from plug cap to plug cap on a coil- have meter on 20 kohm (or higher) scale-what reading do you get?