[Thumper]

What is the metal shield clamped around the ignition wire at the spark plug for?

What is the bolted on shield that bolts onto the cylinder just outside the spark plug for?

I figure I can save .023 pounds if I remove them. Is that OK?

Matt

[LJRead]

I would guess - heat shields - trying to lose weight Matt?  A process begun?  I'd like to lose a little myself.

[scoTTy]

i thought it was for catching electro magnetic waves..  I just thought it was part of the new clean air thing going on..  maybe it gives you better gas milage while it's on..  i was always concerned that I would  get got in a lightN storm and it would zero in on thaT pIeCe O F meTaL......  then again I considered it a fail safe thing that if there is enough rAiN.. to fowL thE plLuG...  afterall the guard is an engine guard for the sPark plug..  and.. if their is enough rain ..

[longstrokeclassic]

The bolted on shield was originally there to act as an air scoop,  to redirect cold air across the top of the cylinder head. 
l believe the UK models do not have them fitted because they are not required in our particular climate.

The metal cover around the spark plug is there to act as an RF shied to avoid interference to radios and TV sets and also assist keep the cap securely fastened to the plug. 
Unfortunately more often than not it causes ignition problems as the spark leaks and tracks to earth via the metal casing.  Just unscrew and relace with a decent item such as an NGK.

When I replaced mine I also took the opportunity to remove the cheap HT lead at the same time and replaced it with an 8mm copper core lead.  I know that the likelyhood of this failing through either use or age is virtually nil.