thespaceman

Thanks for your post. This is exactly what my '15 FJ is doing. I thought it might be the battery, but I'm glad to get a confirmation.

The dealer delivered my bike with virtually NO preload on the forks. There were 6 full rings showing above the top. The front got extremely wobbly with or without the luggage at anything over 80 mph. By 100 it would head-shake very badly.
 
Fork compression / preload: I put in a bit more than 50% compression so there are now 3 rings showing.  
 
Fork rebound: I also went to the middle; the adjuster says "TEN", so I tightened it completely (I counted 12 clicks but it's hard to tell) and then backed out 4.  
 
Rear compression / preload: on 5 of six steps. It's great  when the luggage is on; a bit too hard for without, but it's too hard to adjust to fool with it day to day.
 
Yesterday I was out in the Everglades on deserted roads and the handling was infinitely better. Truly a case of "night and day;" no matter how fast I went the bike felt planted and stable. The conditions were ideal; flat pavement and no wind, but even in the ramps etc. on the way home it was much, much better.
 
One tip: use a 6-sided socket on the fork preload adjustment, not a 16-point. Lay a small piece of blue tape over the top of the adjuster first, then slide the socket over. This will avoid damaging the adjusters, which are very soft. Also put a layer of blue tape on your flat-head screwdriver before adjusting the rebound for the same reason.

You should have heard the crap the Harley mechanics told me when I asked about using synthetic oil in my '77 Shovelhead.  "It's TOO slippery; the bearings will slip!"  "Your clutch will dissolve!" "Don't bring it here when that engine grenades!"  And my favorite: "Harley Davidson says using synthetic oil voids all warranties."
 
So I put in Mobil 1 anyway.  The only objective measurement was that oil temp dropped a good 20+ degrees, but my seat of the pants dyno said it ran better.  And a couple years later Harley started selling their own synthetic oil.
 
I just changed the break-in oil for Castrol full syn at 550 miles.  The factory oil looked like water; if 500+ miles of that crap didn't break the engine in nothing will.