Question for you serious techs, I've got a 919 motor in my 93 frame that's been mildly jetted (so I was told, but not about to go through the headache of rejetting again.) Anyway, running just slightly rich, not fouling the plugs (which are fairly clean after 12k) but still blackening the pipe with carbon and has slightly poor response at mid rpms. I've fixed the drivability issue by upping the heat range of the plugs from a 9 to an 8. The bike has never been stronger, but it does heat up (ECT) quicker. I'm just slightly concerend that the increase of combustion temps will be enough to cause heat related damage (warped cylender walls, burned out pistons, fried oil control rings, etc.) It's not hot enough to cause ping, but still. Does anyone have any experiance with running a hotter plug?

 

If the only adjustment was mild rejetting, stick with stock plugs(heat range). You could change to iridium which will perform better, but the only thing you can do to prevent running rich(if thats the case), is to tune the carbs by adjusting the fule screws. If you're mechanically inclined and have the right tools, you can perform an idle drop procedure which the Honda service manual details efficiantly. Tools: 90 degree fuel screw tool(w/ "D" shaped attatchment), remote TACH(reads within 10 RPM), and patience. The procedure works very effectively, but can be frustrating to unfamiliar hands.

 

Those scews are just your idle air/fuel mixture screws. Jet orifice size is what changes the amount of fuel during wide open throttle. Slide operation is midrange.

If you look at the manual, the "optional" plugs for the bike are both one step up in the heat ranges over the basic OEM plugs. Those shouldn't be a problem. And if it's listed in the manual, then you have to figure it is 100% safe and idiot-proof.

...now if they just made the plugs in a commonly available one step colder for me.