Yamaha Virago Ignition Coil Replacement

Replacing the two ignition coils/wires, caps and spark plugs.

NOTE: I accidentally deleted the video segment on where I pulled the coils out and put them back in. The mounting screw at the front of the coil is removed so that the coil can be removed from the mount - don't forget to remove the caps. From there, the front/left side coil is easy - just route the wire as necessary. For the rear cylinder coil, remove the cap and tape a wire (similar in size) to the end of the spark plug wire before pulling the coil out. This is necessary in order to pull the new coil wire back across the top of the engine and frame since it's a pretty tight fit.

Changing the coils is pretty easy but understanding how all the components work as a system can be a bit of work. I've spent about 20 years as a technician/technologist and electrical engineer working on high frequency, high voltage and high power radiating elements (radar, sonar, satcom) and I've heard and read some pretty bad explanations about cap and plug resistance which can confuse and mislead people trying to troubleshoot a bad spark.

Most early Viragos came with NGK BP7ES (non-resistor) plugs which are discontinued and hard to find. NGK now specifies the BPR7ES replacement which is a resistor plug with 5K ohms (5,000 ohms) of internal resistance. Since the original spark plug caps had a 5K ohm resistor built in, using any brand of resistor plug adds another 5K of resistance to the system. This causes a further voltage drop leading to a weaker spark and misfires. To make matters worse, some Virago caps had a removable resistor/spring combination that was prone to corrosion.

Resistors in caps and plugs are there only to suppress RF ignition noise (they have no other function) and only reduce spark intensity. If you can't find a non-resistor type plug, you can remove the cap resistor or simply experiment with other values. Once I installed and tested the aftermarket coils, my final set up was the NGK BPR7EIX Iridium spark plug and NGK LB01EP cap. This setup has proven to work well and with the carbs properly tuned, I'm now getting very good engine performance with strong throttle response and no misfires or backfires.

The OEM Yamaha coils are also hard to find and I ended up sourcing something that works, but the voltage and igniter trigger pins are in the wrong location. Details about how I had to work around this are shown in the video.

For proper coil primary & secondary resistance values, check your service manual for the actual specification and verify that the spec is to be measured with or without the cap resistance.


Link to the coils:

https://www.aliexpress.com/item/40013...

Link to the caps:

https://www.amazon.com/NGK-LB01EP-Spa...