XZ 550 spark plugs

Standard for the Euro XZ are NGK DR8ES-L spark plugs. This code implies it is a D type plug (12 mm thread with 19 mm length for 18 mm socket [ES]) with R = a Resistor. The warmth grade is 8.

The R of the DR8ES-L is not for Racing, but for Resistor!

Standard Euro cap without resistor (NGK T-131) and NGK DR8ES-L spark

plug with built-in 5kOhm resistor. Other side of spark plug in the picture

above.

US XZ550’s have a D8EA spark plug, that is a plug without resistor.

The US models, however have the resistor in the spark plug cap. In both cases it is 5k Ohm.

The caps that were on our 1982 Canada bike have built-in 5kOhm resistors.

This seems to be standard for US bikes, (see Haynes ill 6.5 on page 112).

So US bikes have the resistor in the caps (first mentioned to me by Lucky on

www.ridersofvision.net), Euro XZ’s have the resistor in the spark plug itself.

In both cases the resistor value is 5kOhm.

Some XZ’s have problems with starting up, due to the 14 Amp/h battery that has not so much reserve power, XZ carburetors that do not give the ideal mixture under all conditions, cold oil etc. The general practice in my XZ’s teached me that a bike without a resistor is a better starter under critical conditions.

Advice: US rider, buy caps without resistors such as they are standard on the Euro XZ, that is the NGK T-131 plug cap.

For Euro riders, do not use any more DR spark plugs, but D spark plugs.

Warning: for riders with GPS systems riding without resistors may cause problems. Also the neighbor’s radio may have interference when you start up your XZ.

Warmth grade

The standard warmth grade is 8 for all XZ550’s in a scale between 5 and 12. Five is a warmer plug, 12 a colder. For the XZ the 8 grade seems to be a rather cold choice. It keeps clean when the engine has to work really hard. If not, it seems not to burn all combustion residues, resulting in more difficult starting.

For this reason I use since years the D7EA plug in all bikes, except in the sidecar-bike. That engine has to work real hard and the spark plug color indicates that a 7 plug is too hot. A 8 grade is OK in that bike.

If you want to go the luxury track, there are expensive iridium plugs: the NGK DR8EXI (see photo below) in the 8–grade and the DR7EXI in the 7 grade. Note that these are R-plugs, plugs with an internal resistor. If you are in the US, don’t use these in combination with the 5kOhm standard caps. This might be the better plug for a rider in need of a “resistor-plug”, for instance of you have a GPS system on your XZ. The technology of this iridium plug makes up for the loss in spark strength by the resistor.

NGK iridium spark plug of the 8-grade: the DR8 EXI plug. Photo from NGK website