Resistance spark plugs? Yamaha engine

[Heron Addict]

I have a couple of Yamaha/Mariner 2hp outboards. I am running an NGK B5HS spark plug in the old 1984 model, which has points. I have now got hold of a much more recent 2002 one which has CDI ignition (it looks almost new!). The cowl has a sticker saying to use a NGK BR5HS spark plug. The handbook says BR5HS but then with B5HS in brackets after it. I assume I can use either. What is the difference in practical terms to running a resistance or non resistance type spark plug? Are there circumstances where one should be used rather than the other?

[david doyle]

Can't really answer your exact question but maybe this is of some interest......

Pre 1995 2hp / 43cc yamahas made in the USA called for a B5HS or a L90-C Canadian and European ones called for a BR5HS
Gap .024-0.028

96 models went to B7HS or L90C with the same gap.


I have the service manual for 84-96 yamahas if it would be useful to you or if you need any more info on your older ones.

[phil]

On a CDI ignition it probably does not make much difference. Resistor plugs are for the suppression of radio interference noise. Do you want to listen to your radio while motoring in your boat? Also the possibility in densely populated areas of interference with other folks listening pleasure.

They are definitely not recommended for the older points style ignitions due to the higher voltage required to push an adequate spark through them. They likely would not do the rfi job unless combined with carbon fiber ignition wires which are an even bigger no no for points based ignitions.