1981 GSX400 spark plug confusion.

[Polish-Jack]

I am confused about what spark plug is best to use in the GS(X)400 I am trying to get to run. Using the addendum service manual that can be found on BikeCliff's site it specifies on the GSX400E model to use either a D8EA or DR8ES-L, then on the GSX400S, GSX400L, and GSX400E/S it removes the D8EA specification and only gives you the option of a DR8ES-L. Then for the GSX400T removes the DR8ES-L specification and only gives you the D8EA as an option.

GSX400E - D8EA or DR8ES-L
GSX400(S)(L)(E/S) - DR8ES-L only
GSX400T - D8EA only

Is far as I have been able to find out the engine in all five GSX400 bikes that appear in this manual are exactly the same, so why is there spark plug shuffling going on? To make matters worse, I am not sure exactly which sub model I have. It's either the E, S, or E/S, and the only spark plug I can get locally here is the DR8EA instead of a D8EA. I'm told at the local shop that the D8EA and the DR8EA are the same with the R version only having a resistor in it to prevent EM interference and that there will be no difference to the bike. That then begs the question of why they recommend a different plug all together when adding a resistor to the plug?

I'm confused...again.

 

[fastbysuzuki]

The spark plug caps will likely have a resistor built in so you do not want spark plugs that have a resistor. Either way there is no real need to have a resistor many on here remove the resistor from the plug cap and replace with a piece of brass or copper or welding wire the same size as the resistor and run a non resistor spark plug.
look at post #4 in this link. https://www.thegsresources.com/_for...-plug-caps&highlight=Remove+plug+cap+resistor

 

[Gorminrider]

It's odd-you could look up the differing NGK plugs ...but I think they all cross refernce to the Nippon denso E24ESR-U so differences are slight. It could just be a random mistake too. I can't tell the difference using them.

as to E and S, I think I've read here that the S will have mounting points for the headlight fairing and that's the only difference. It won't show in the VIN .

 

[Polish-Jack]

So I had a genius idea and took a look at what the previous owner had installed and they were DR8ES-L plugs so I guess I'll stick with those.