"Resister" plugs and or caps, and wires?

[Clifton]

I thought I'd replace what I believe are original plug wires on my 1993 R100R and find there are 1K ohm and 5K versions, as well as 5K resister. Plugs offered are BP6ES and BPR6ES, with the "R" being resister I presume. Should I be using 5K resister wires and also BPR plugs? Sorry I know nothing about 12v wiring.

 

[timeandtide]

I thought I'd replace what I believe are original plug wires on my 1993 R100R and find there are 1K ohm and 5K versions, as well as 5K resister. Plugs offered are BP6ES and BPR6ES, with the "R" being resister I presume. Should I be using 5K resister wires and also BPR plugs? Sorry I know nothing about 12v wiring.

Sorry can’t help - way above my pay grade!

 

[Gelandestrasse]

You don't mention what plug caps you are using. Read up and your answer may be here: https://bmwmotorcycletech.info/sparkplugs.htm

 

[Clifton]

Thank you Gelandestrasse and I see written there:
"From 1981, BMW used an electronic ignition. Nominal 5000 ohm spark plug caps are a MUST on those, to protect the ignition system."

 

[SBD]

I would not expect that you would want resistor plugs as well as resistor caps.

 

[Clifton]

SBD good point and you're correct according to Snowbum's site.
"If you install both resistor plugs & resistor caps, your spark can become too weak to reliably fire the mixture 100% of the time, particularly in later leaner-running Airheads. This has been seen with 5,000 ohm caps & resistor spark plugs being used at the same time."

 

[Bubb]

I’m with SBD…. Resister plug caps, but NOT with resister plugs…..either/or I believe.

 

[Gelandestrasse]

I’m with SBD…. Resister plug caps, but NOT with resister plugs…..either/or I believe.

Snowbum recommends you get your resistance from the plug caps, not rely on the plugs (he lists examples of where he has measured the resistance of so-called resistance plugs and found them very variable. I am indirectly helping a friend out who has melted his coils due to relying on resistance plugs which, when tested, are severely lacking. So my recommendation would not be 'either/or' - you just can't rely on the plugs. Go for the plug caps. 5K Ohms on a standard setup.

 

[Clifton]

Thanks. I have these on order, hopefully they are correct, and will use regular plugs that are not resistor.

Metal Caps - 5K Ohm BMW R Airhead Ignition Cable Set 12 12 1 243 453 / EnDuraLast

Copper multi-strand inner core wire - 2 x 18 inch / 40 cm length leads 7mm silicone jacketed copper cable wire (with no printing or branding -'classic' black ) 5k ohm metal resistor spark plug boots 12 12 1 243 453

www.euromotoelectrics.com

 

[SBD]

Looks ok to me. If they’re to spec, it should be fine.

I’m very surprised by “melting coils” as a result of no load resistance. A spark gap, by its nature, has a very high resistance (not infinite, but very very high) until the breakdown, then it’s pretty low until the charge has passed, and the ionisation decays. In an engine, the ionised gases are burnt or shot out of the exhaust anyway.

The resistance does several things: it reduces radio interference, it will dissipate some of the charge as heat (rather than “spark”), and it means the breakdown voltage at the coil will be higher, and the “end” of the spark will cut off.

The total charge in the coil will still be dissipated every cycle, so I do not know how a resistor in the spark circuit can possibly affect the coil.

If you had a coil that was designed to be used with a ballast resistor, and you didn’t use the resistor (in the primary charging, circuit), that would definitely melt the coils.

 

[Clifton]

SBD you're talking way above what I know about spark ignition systems (which is about zero).
All I know is the bike started and was idling maybe 3-4 seconds then quit. I pulled the plugs, spun the motor with plugs resting on the fins, and neither show spark. I used this opportunity to order a Wedgetail Ignition kit and when installing it I'll pull and clean every connector as well as replace the plugs and wires. Fingers crossed.