Hi, sorry for not replying immediately to this interesting debate.
Well, what can i say...When i did the flapper mod, i got an immediate advantage at very low rpms (under 3500 rpm, so to say). The V4 is not the smoothest engine at those rpms anyway, but now it's much better. Don't know why it behaves in this way, it should be the opposite (open flapper valve = roughest behavior at low rpm), but currently i will keep the flapper mod.
Snorkel mod - just a matter of better noise 😉
Gas mileage? It's always the same - bad. You go slow, you go fast, it seems that the injection system was originally set to always squirt as much gas as possible in the cylinders, regardless of the conditions. I drove my bike for half tank at hilarious city speed (3000-4000 rpm) and the result was always the same , a miserable 235 km (146 miles) from a full tank, excluding reserve.
Just yesterday i heard another 800 Fi owner - he had one non-catalyzed (1998) and one with catalyzer (2001). Well , he said exactly the same things - the '98 has a better punch at midrange but has crap mileage and runs always quite rich (the exhaust is always a bit blackened after some hundreds of km).
Fuelly mainly shows results from US bikes, the few non-US bikes have worse result about gas mileage. Exactly for this reason, i would like to know if there is some differences between the 1998-1999 Italian-European ECU and the USA one.