The Fly 150 spark plug access design is not user friendly. This applies to my 2010 model. The engineers did not do a good job of designing this model for the 'do it yourself" owners. That being said, I have the time and the tools to do all of this, so I plunged into it this summer and will be doing everything, and hopefully become somwhat of an accomplished service/repair individual and contribute to the Vespa Forum in a sensible way, unlike some on that site who can't answer a simple straighforward question.
Remove spark plug a long job but well covered in the 17 pages in the shop manual book - to which I have to add photos and more descriptions - such as pix of rear shock and explain how to remove it because the shop manual is not user friendly.
Note: remember spark plug is set in at an angle and you are screwing hard steel into a soft allow engine head - screw in slowly by hand at first.. if any resistance is felt, just back off and start over. Just screw it in carefully by hand and set firmly with plug socket that came with scoot tools ..photos to be added - not overtight.
Photo of useful tools to have handy (a) small magnet on thin wire to lower into areas to pick up dropped screws, and (b) long thin claw tool to pick up same screws...these two tools will save you the time and agony of looking at a screw in an impossible area to reach with your fingers.
Here are my first photos of the rear shock which has to be removed/ raised to drop engine - that is according to the 17 page workshop manual pages I have. Single click on my pix to enlarge.
Pix #1 below is the view down into the rear of scoot showing the rusty top nut/bolt of the single rear shock.
pix # 2 below rear shock bottom should swing out towards rear when bolt/nuts are removed...or does engine just drop.
pix #3 below just another view of rear single shock on rear left of scoot.
ok...so now i have to identify the important parts.
in pix #2 & 3 above the outside nut on rear bushing above tran case is 1/2 inch. I have to test the inside nut which will need a long depth socket about 3/4 inch size...I think it is 17mm... or a wrench of same size to hold nut while loosening the outer nut...easily done.
and done with top nut/bolt of the shock still firmly untouched in place...but eventually make sure engine with wheel attached to engine drops slowly and carefully...who knows???