What the others experts have said.
Oily/milky liquid is usually water mixed with oil which could just be the MMO mixed with water from spinning your engine.
Check your engine oil for this milkiness as well. If that is milky too then you have a few engine oil changes in your immediate future.
If you have a water lift muffler on your exhaust side it is probably still full of water and may be slowly draining back to your engine, into the exhaust manifold and somehow finding its way into your carb.
As Faster indicated, the water is forced out of the engine by the engine actually running. The combustion gases from the cylinders helps to push the water out the exhaust when the engine is actually running. So, yes, you should put the plugs back in and try to fire it up (with the raw water valve closed) to push (not drain) the water out of your exhaust side.
I guess you will be closing your raw water intake from now on. Often I will wait for the engine to start turning over before opening the cooling water intake valve.
More diagnostic questions:
- How long have you owned this boat with the A4 engine?
- Has it ever had any performance problems in the past?
- Are you a member at the Moyer Marine (A4) forums? Moyer Marine Atomic 4 Community - Powered by vBulletin
and do you have the A4 owners manual?