Got a Briggs 17.5hp single cylinder that was full of water.  I drained the water, freely turned the crank by hand, pulled the plug, ran carb cleaner through the cylinder and oil res, valves, etc.  Everything I could reach without pulling the head.  Cleaned the carb and turned it over a few times with all the plugs out and valve cover off to get anything out that didn't belong.  Buttoned everything back up, filled with correct amount of oil, again, correct amount of oil, it is not overfilled.  Checked for spark, got great spark.  Put the plug in and gas to the carb and tried to fire it up.

I get smoke from the exhaust and the exhaust return tube that goes into the air cleaner.  It tries to take off but just won't catch.  A couple times it fired fast enough to disengage the starter.  There is a lot of oil coming out of the exhaust return tube.  Does this mean I have a bad head gasket/cracked block/sleeve?  Shouldn't be that much oil coming out of there, it would drain right into the carb.  I don't have a compression tester, but I note a distinct difference between how hard the engine turns with the spark plug in or out, so there is some compression.

Any ideas?

Stuck or broken rings would be my guess.
Pull the plug and plug the hole with your finger. The compression should blow your finger out of the hole forcefully.
Or you could use a compression gauge, but what's the fun in that.

if the cylinder was full of water, all sorts of bad shit could have happened





how long was the engine sitting?  if nothing catastrophic happened, you could just have a sludged up carb


tear it down and clean everything, pay attention to the jets
 

First guess is blown head gasket. As Briggs engines are equipped with a compression release, using a compression tester really isn't a good test. Unless it is really bad the engine should start even with a blown head gasket.

How did water get in the cylinder? Sounds like a carb problem. They are easy on the B&S motors. There is a "governor" on the carb, but in reality it is a gasket. Be careful with this when you take it off.

I completely serviced the carb short of actually replacing the float.  It's not the carb.  Cylinder will blow my finger off the spark plug hole without trouble.

I don't think there was any in the cylinder since it hadn't seized.  But the oil res was full of water.