faff: activity without immediately beneficial effect on the object being faffed about - though during the faffing the faffer might (or might not) learn something which he can later use to more effectively
fit - to make individual parts into a whole which works. This may or may not involve modifying, or occasionally making, the parts.
fettle - to take a fitted whole, as above, and make it work well, smoothly, or even beautifully.
? ah well