After a fun high speed run last Sunday (6-8 min), I noticed a bad vibration the next time I started the boat up. Need help in figuring this one out. Here area the facts:
1993 Formula 271SR1
Built Gen6 540 by previous owner, estimated 620hp. Less than 100hrs
Bravo XR Drive. Less than 100hrs
Full Hydraulic steering

Vibration is similar to an airplane flying over your house too closely or going over rumble strips on the HWY at 20mph.

Vibration shows up even in Neutral
Is worse when trying to turn
Engine fires up fine
Will run WOT @4800rpm. Seems to make speed, didn't run too long at that RPM to see top speed
Good oil pressure (60-75psi) per gauge. Has always read that
When you accelerate the vibration comes and goes as you go through the RPM ranges
Changed spark plugs, no difference
Did notice that the oil was low by 3quarts out of a 14qt pan. (I failed to check oil past couple of trips out, I know. I'm an idiot on that)

Like I said, vibration is bad. I was hoping it was a bent prop, but since it is there at idle in neutral. I guess I can rule that out.

Any help is greatly appreciated.
I am praying it is not an internal engine problem

I'd pull drive and check ujoints and gimble bearing..like now.

BTW: 3 quarts low on a 14 quart system still has 11 quarts in it. This is a non issue.

Check your motor mounts too.

Yep pulling the drive tonight. Will probably try to rig a water source up so I can run the motor with out the drive to help isolate further.

Hi probability of a bad u-joint as they spin even in neutral and would complain more when loaded in a turn. Checking motor mounts is a good idea.

Thanks adding mounts to the list. Anyone offhand know the torque spec on the mounts?

U joints or gimble bearing.

Let's us know when u you pull the drive. Hopefully your gimble housing is still in one piece. Regardless it would seem as though your u joints are gone. Like disintegrated gone if it's anything like your implying. Gimble bearings typically give warning and tend to make more bearing notice rather than vibration although anything possible. I'd replace everything while off even if it's just one or the other.

Did you check your props?