my ? is simple what are the differances between a hot or a cold plug what are the reasons for running one over the other.

 

One will give you a hotter spark. Used to make fine tuning for rich or lean conditions.
1. You set your heat range from the ground strap (this is the piece closest to the piston)
2. You do all the plug readings for jetting from the base ring (the base ring is what the ground strap is welded to at the end of the threads)
3. You determine detonation and timing issues from the porcelain (the porcelain shows preignition/detonation, it will not accurately determine jetting / air/fuel
ratios) DO NOT BASE JETTING DECISIONS ON THE PORCELAIN COLOR AT THE TIP.

1. How to determining plug heat range:
The ground strap is your window to getting this right. If the "color" of the ground strap "changes" too-close to the ground strap's end, (the end opposite of the base ring), then the heat-range is "too-cold" (heat transfer is too quick to the base ring). If the "color" of the strap changes near where it is welded to the base-ring, then it means that the plug heat-range is "too-hot" (heat transfer to the base ring is to slow causing the deposits to be burned off the strap completely). The strap at this point could start working like a "glow-plug", probably resulting in pre-ignition and/or detonation. The properly set heat-range is when the "color" is at the half-way point on the strap.

 

thanx very helpful