GP Customs
I)Cylinder heads: So lets talk a little about cylinder heads
                             and how they work and why!!!!!

*Its important to understand that the volume
              of fuel vapor and shape of the head when
              in proximity of the piston can be a very....
              good thing or bad with regards to                                    
               performance. It is therefore worth a basic
              understanding of what not to do even if you
              only have a basic understanding..........
           *Ok well remember when you were told that
             higher compression was good? Well the truth
             is that with high compression comes higher
             dome temps/detonation and pre-ignition.
             What you need is a good combination of squish
             and volume.

Squish: The area surrounding the combustion
                         chamber where things get rather close
                         between the head and piston.
           * Ok so why a squish area?...Well there are a
               few good resons.
                       1)move the mixture into the combustion
                       2)reduce the ability of flame spread onto
                           outside of the piston and reduce
                           compression temps.
           * But alas with the squish doing a temp and
               combustion control job there is the loss of
               unburned potential power lost in the outside
               charge that resists burning.
Best settings for           
(91-99) machines seems to be 7.5-7.9cc.
 Squish should be set .026 to .028 of an inch.

Combustion Chamber: Yes its the area                             
            surrounded by the squish band!!!! This pocket
           does most of the real work and depending on
           bike you own it could employ anything from
           a hat-section,conical to a torus-type chamber             

Plugs :Plug position in the combustion chamber
           is also a very important item to monitor as
           the goal again is not to screw with the                              
            combustion. So you keep it as close to the roof
           of the chamber as possible. The more it                           
            protrudes the more inefficient the flame spread
          across the pistons dome.
Read plug for timming by the burn pattern on            
the electrode tip. 3/4 to 7/8 from tip to plug will
           be silver in color for correct ignition.

See tuning log for a useful item for reading plugs