7 is a 'hotter' plug, meaning it has a longer ceramic insulator, reducing the amount of heat dissipated by the tip.
All is explained here;
http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp
I can't find the link with exact details, but I remember reading prior that 1 heat range is approximately 40 centigrade.
My bike almost always idles forever, this is using the jetting and oil ratio in my sig. This is also before swapping the plug, my problems tend to be at higher rpm, but... (read on)
Loading is 2 things -
1 - Excess oil remains in the bottom of the crank from a period of low rev riding. This oil is always there, even at high rpm riding, but the level can increase when lugging. When you crack the throttle open, this oil gets sucked into the combustion chamber and causes a burbly top end until the correct level is reached.
2 - If a spark plug is run under the 'self-cleaning' temperature for too long, an excess of conductive material binds to the insulator, allowing the electricity required for spark to short between the insulator and earth (cylinder), this can cause very similar symptoms to the above when wide open throttle, once the plug reaches temperature this coating will burn off. (it is more difficult for the spark to arc between electrode and spark point as the revs / pressure increases, hence this is more noticeable at high rpm)
Problem is with our bikes being the bad boys they are, it is very rare you run above 3/4 throttle for any sustained period. Thus the plug rarely reaches or stays at it's 'self-cleaning' temperature. This is likely to bring about problems such as, difficulty starting, poor idle, burbling/lurching at mid rpm, and sputtering at high rpm.
. Try raising the clip 1 notch.
