Britbike forum Forums Thread Like Summary - NGK Resistor Spark Plugs

Any of you guys have an opinion about using the NGK BR7ES or BR8ES spark plugs with either points or electronic ignitions in our vintage British twins? Apparently NGK has discontinued the B7ES and B8ES, as well as the projected-tip versions, BP7ES and BP8ES.

Digital ignitions usually need either resistor caps or plugs but analogue ignitions do not although EI manufacturers often recommend they are used.

http://www.boyerbransden.com/faq.html
FAQ:
"Why Do I Need To Use Suppressed Plug Caps?
MKIII and MKIV do not require suppressed plug caps for operation although we recommend using supressed 5000 ohm plug caps. Micro Digital and Micro Power units must be fitted with supressed plug caps. Plug caps fitted with suppression resistors are usually fitted to prevent radio interference. Radio interference (noise) can cause more complex electronic circuits like radios and computers to malfunction.

Our Micro Digital and Micro Power ignition systems contain a small computer operating at high speed that can be adversely affected by radio frequency interference. Symptoms can range from refusal to start to intermittent engine stalling symptoms. Use of non-suppressed plug caps has been known to cause permanent damage to the ignition unit."

Resistor plug caps or plugs required?

Boyer Micro MkIII, MkIV = No
Boyer Micro-Digital = Yes
Boyer Micro-Power = Yes

Pazon Sure-Fire = No
Pazon Altair = Yes
Pazon Smart-Fire = Yes

Tri-Spark = Yes,
Lucas Rita = No.
Wassell Vape = No

My experience (rather than opinion) is that 5 kohm in the HT circuit makes no difference to the performance of points or electronic ignition.

Recently I’ve been using a dual output coil with two resistor spark plugs, so that’s 10 kohm in the HT circuit. It works just fine, with Wassell electronic ignition.

Because I fancied fitting iridium plugs and couldn’t find them without resistors.

Be as wise an ass as you want- you’re not going to offend me!

Just use B7EV or B8EV plugs instead of ES type.

This aeroplane guy did some rudimentary tests, which don’t really answer the question about any palpable effect of low value resistor (5,000 kohm) in an old bike, but still quite interesting.

http://www.viragotech.com/fixit/Resistor%20spark%20plugs%20and%20resistor%20spark%20plugs%20caps.htm

I'm sold on Denso. I had a problem on the 68 that only happend upon leaving a certain stop sign after a hard uphill canyon run and needing to to cross four lanes of speeding truck traffic. The bike would stutter a bit. Not much but at certain times it could be heart stopping. I chased that stutter for years. Denso cured it.