i agree with the comments on oil inj, as long as you KNOW for sure its working. you'll probably know right away since if your doubling up, it will probably smoke like a mother ! (not to mention if crank seals are leaking, you'll scare your neighbors, they will think your garage is on fire)
but 2x check to be sure its working, and again, they are generally considered very reliable.
I ran premix from day one, but I was an old school yamaha rider so I was very comfortable premixing, and didn't think twice about it, and honestly even with all my riding, I never fouled a set of plugs. (even on my present yami, which I premix very thick at 32-1, i'm still on my original set of plugs and i've put almost 70 hours on the ski)
would I premix my next seadoo ? you betcha.... i don't care about the smoke, its behind me... and I prefer to burn an extra $50 in oil every 6 months to a year over the cost of an engine, but that's just me, and my personal preference. (and I prefer amsoil just to throw that out, check out the dealer trial for $10 and have it shipped right to your door)
re: tempo, they must go, and if it run's during your "test" but run's poorly, they might be the cause, even yanking one line and looking for green goo will tell you immediately if your looking at some bad lines, but even if they look clean, if you plan on holding onto the ski, they must go.