Spark Plug Heat Rating ???

I'm a tad confused, normal with me I guess as i'm getting older by the minute , I have Iridium plugs (BPR6IEX) in the bike at present, they've been in there for quiet a while now, I took them out the other day and cleaned the build up on them as a set of carbs I had on it were running rich for a while, I changed carbs and fuel economy is better ... blah blah blah .... anyway I was thinking of putting new "normal" plugs in, so I had a look at some NGK BPR6ES (pretty sure it has the screw cap???) which i'm pretty sure are the plugs to suit the 13, please correct me if i'm wrong, then I thought about putting Denso plugs in it instead of the NGK, went to the Denso site and put in the make and model of the bike and it gave me a Denso plug W24ES-U (this has a heat rating of 8 in NGK), can someone please do a list of plugs suitable for a 13 in different makes of plugs ??, or is it ok to use the recommended Denso ones or the ones they say are the same as the NGK plugs ???, Please someone let me know and maybe others who are as confused as I am , thanks in advance ... Pete.

P.S. Is the R in the NGK plug for a resistor ??? and why do we need a resistor plug ????

The Denso equivalent to a BPR6ES is a W20EXR-U from what I can find. It would take a lot of talking to get me to change from NGK.
The ignition was designed around a resistor plug and not using them can lead to overheated coils and in some cases a fried final amplifier transistor in the ignition system.

I would always start with the manufacturers reccommendation for spark plugs and if you really want to run an alternative spark plug go with the cross reference and not the alternative spark plug manufacturer's reccommendation for a certain application. I definately would not go for a hotter plug. If you go with a plug that's too hot, you take the chance of burning a hole in a piston caused by detonation. Shitty fuel, oil burning conditions or low compression will cause build up on sparkplugs. When the proper heat range is selected, the plug is allowed to get hot enough to burn off the residue build up and yet stay cool enough to not initiate combustion prematurely.

Carbs VS. Fuel Injection - Carburertors will always be somewhat out of sinc. You will never get a carb set up that will run great under all conditions. Air temperature, fuel quality, engine temperature, air density, humidity, power requirements etc. will never be met ultimately with a carb set up. Only the fuel injection will accommodate all or at least most of the conditions depending in the fuel injection components. If the fuel injection measures the O2 levels in the exhaust and maps the fuel based on O2 readings then the system will come close to optimum.

There is a process for dial ing in a set of carbs. Get the engine up to running temperature. Put in a fresh set of plugs. Run a quarter mile sprint at full throttle and immediately shut off the ignition and coast to a stop. Pull the plugs and read them (look at the color) Ash Brown is desired. If they are more to the black color, you need to go smaller on the main jets. If they are more to the whitish color, go one size bigger on the main jets. That's the main jet size sorted out.
Next you need to sort the throttle bore needles (better known as the main jet needles). Again with a fresh set of plugs, go out for a 10 minute ride and then kill the ignition. Pull the plugs and take a reading. Again you're shooting for ash brown. If the plugs are more black, drop the main jet needles one notch. if the color is more to the lighter side of brown or whitish, you need to richen up the mixture by raising the needles one notch.
From that point on you can monitor the spark plug colors on a regular basis when you normally change out plugs.
Altrernatively, you could buy a wide band O2 sensor and take readings of the exhaust under many conditions while driving. This is my preferred way. A wide band will run in around $140.00 and can be incorporated into your instrument cluster. That's the way I'm going.

Important to know !
<"NGK Spark Plug Heat Rating
The spark plug heat range has no relationship to the electrical energy transferred through the spark plug. The heat range of a spark plug is the range in which the plug works well thermally. The heat rating of each NGK Spark Plug is indicated by a number; lower numbers indicate a hotter type, higher numbers indicate a colder type. >" (From the NGK site)

I believe NGK is the only plug manufacturer who's Heat range index #'s go down as the heat ranges increase.

For 36 yrs I've set the idle by ear. An arbitrary 3.5 turns and then some minor tweaks to get the idle sounding it's smoothest. The color on the (NGK BPR6ES) plugs was always in the "Tan" range. Then broke down ( cuz the price was too good to ignore) and bought a Gunsons Color Tune, recently - just for "Shits & Giggles" Photos are after a first and second C. T. adjustment and "Chop". Need some tweaking I think !

scotch wrote: For 36 yrs I've set the idle by ear. An arbitrary 3.5 turns and then some minor tweaks to get the idle sounding it's smoothest. The color on the (NGK BPR6ES) plugs was always in the "Tan" range. Then broke down ( cuz the price was too good to ignore) and bought a Gunsons Color Tune, recently - just for "Shits & Giggles" Photos are after a first and second C. T. adjustment and "Chop". Need some tweaking I think !

I just recently ordered a C.T. and a little carb sync tool - I'm eager to be able to use them. By any chance do you know if, on the kz13, you need to have a carb sync tool with six dials, or just 3? I was thinking I would only need 3 for it having 3 carbs, but now I'm guessing maybe it's supposed to have 6 instead?