The oil specified for 999 Fire is 15W40 API-SF. The API code refers to the grade of additives and detergents present in the oil, it has nothing to do with its viscosity.
I recommend plain mineral 15W40, preferably API-SG and better. I have been running my 45 on 15W40 API-SL for ages (well, 7 years) with no problems.
I never felt any desire to experiment with semi- or full syntetics. From what I gathered, there is a danger of these oils dissolving the carbon deposits in the engine.
IMHO it is more useful to change the oil and oil filter more frequently. I do so every 10k km just for the feeling of spoiling the engine

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The spark plug gap mentioned in original manual is from 0,7 to 0,8 mm.
With regard to what turboned said, my bet is that if you set them to 0,7, you cannot do wrong
