Correct Spark Plug Heat Range

[Jim Crenca]

The shop manual for my 1994 KDX calls for a B9ES spark plug yet most of the posts refer to B8ES. Do the newer bikes use a different plug? Also, is there ever a need to change heat ranges due to engine mods (like pipe, silencer, airbox, or RB Designs carb mods)?

 

[MADisher]

95 and newer service manual calls for the BR8ES.

Anyone know off hand the big diff between the BR8ES and the B8ES. (I know R=resistor plug) but what's the impact of using a NON-resistor plug when the bike asks for one ?

(I have lots of the BE8S, as that is what I feed my RM regularly :p )

 

[agitt73]

a b9es is one step of colder plug then a b8es;)

 

[BRush]

The resistor plug is intended to minimize EMI (Electromagnetic Interference). The more sophisticated the bike's control module, the more you have to be concerned about EMI. If I owned a something like and '01 YZF250, I'd be careful about sticking with a resistor plug, but IMHO, the KDX is not that complicated. I have put on many miles using B8ES plugs without any ill effect. I've seen one or two posts by KDX owner's reporting a high-rpm miss when using a non-resistor plug, but I have never experienced this myself. I currently run a BR7ES - since if you're buying a new plug and a resistor plug costs the same as a non-resistor - why not make the owner's manual happy? If, however, a case of new B7ES plugs fell from the sky, I would not hesitate to use them.

 

[joe woj]

ive never run a resistor plug in my bike have never had any problems, the higher the number the "colder" the plug, the lower the number the "hotter" the plug, im pretty sure i read somewhere that its a diffrance of about 30 degrees in the cly per each step, so i run the 8 in the summer, and then switch to the 7 when temps drop below 65, to keep some heat in the engine, this always seems to work well for me.:cool:

 

[canyncarvr]

I've noticed some troubles with a 'non-R' plug.

My DiscMan kind of whines past about 4k r's, my radar detector gives off some false Z-ray detections. My portable HDTV does ok..but the NTSC unit I had earlier had some raster squiggling issues.

My MP3 player worked great...well, up to my endo in the mud last weekend. It doesn't work at all, now. ;)



Keep in mind that a change in heat range of plug also correspondingly raises/lowers engine temperature. Up to 50º! That will explain why your bike starts gurgling and puking out the overflow on that uphill after you change from an 8 to a 7.

 

[MCMAN56]

I tried running the B9ES in my '92 KDX200 per the manual. However, it would foul a plug after about 20 miles of woods riding. I switched to the B8ES and have never had a problem since.