Spark plug cap

[Blurredman]

Hi Guys,

I'm looking to replace my spark plug cap as the one on it now is very worn to the point that engine vibration managed to allow it to come off. This hasn't actually caused me any issue as it continued to run but with the cap just resting on the contact. However it is not ideal.

I use a typical BR7HS spark plug. What is the appropriate Champion or NGK cap for it please?

Many thanks.

[MZCountryRider]

Since you're using a resistor plug, I'd either use a non-resistor cap (no recommendation here) or switch to a B7HS plug and NGK LB05F cap.

[Blurredman]

Thanks MZCountryRider.

I have bought the appropriate cap and it is working nicely and is snug. Thanks!

[Tarwetijger]

Just for future reference, it is quite easy to remove the resistor from the cap. Replace it with a tiny steel or brass rod.

[Puffs]

Thanks for the tip!

Does the standard ETZ ignition (battery/breaker/coil) actually benefit from a resistor, either in the cap or in the plug?

[Guesi]

The resistor is mostly important for radio interferences, not for the engine.

MZ recommends a non resistor spark plug and a spark plug cap with 1 K-Ohm Resistance.

[Blurredman]

Hello,

Tarwetijger, I am well aware of the importance of knowing that a lot of the older caps (not sure about new ones) have removable resistors, as I have had to do this and replace them on my Honda CX500.


I do however for vibration issues recommend the more standard car type cap with only one large nipple instead of the small ribbed shaft that you find a lot on motorbikes. It's not fallen off yet!

[Puffs]

Ta for that clear answer Guesi!

Makes sense: the resistor limits the current pulse in the secondary winding of the ignition coil, but the amount of energy in that pulse is quite small anyway, so that it wouldn't do any harm if left unrestricted. I suppose the same applies for more modern ignition systems, like Vape's non-battery based ones, and of course Hall sensor based ones use the original coil.

[AlanJ]

Hi M,
That small ribbed shaft I think you will find is the thread for the dolly type nipple which I suspect has been left off as a cost saver by the manufacturers, but to be honest that's just a guess.
Wish you well Alan.