Gas hydro-locks engine. OMC 5.7

[Cruisers460]

OK, haven't fired the boat (Cruisers 26' Holiday) up in a couple of seasons due to gas tank repair. Today I started it up in the yard on muffs. Barely ran before it locked up. Thought at first I'd screwed the winterizing. Pulling the plug from the #7 cylinder showed it was full of gas, about a small Dixie cup full. Engine would fire and lock, I found the carburetor overflowed from the center, as the boat was on a hill it flowed out of the center into the back ventricles. Carb was installed new about three years ago, not sure about the fuel pump. When i thought to look at the site tube (after having drained the cylinder) the tube was empty but appeared sucked closed near the pump. Any wisdom before I start rearing down the carb or replacing the pump? The engine hydro locking throws me, it seems like the gas would exit through the exhaust valve.

 

[GA_Boater]

When the intake valve is open, the exhaust valve is closed. So on the intake stroke the raw gas is doing it's best to fill the cylinder and as the intake valve closes at the start the compression stroke, lock because the fuel doesn't compress much. Just like water.

Look at Bondo's avatar, it shows the stroke and valve relationship. http://forums.iboats.com/member/8396-bondo

Sounds like stuck floats or needles from here. A quick and dirty way to check the float/needle is to temporarily hook up an outboard tank with a primer bulb, bypassing the pump. Jury rig a direct connection to the carb. Pump the bulb and if it doesn't get hard, it's floats and needles. Of course you need a tank and hose with a primer bulb.

 

[Maclin]

Depending on the brand of Carb, there could be welch plugs in the bottom of the fuel bowl, they are just glued/epoxied in and can begin to leak over time dripping or even dumping raw fuel from the fuel bowl right into the manifold. Sometimes on a rebuild that type of thing is missed. If the needle/seat is not shutting off fuel flow then you will see the fuel come out of the vents. If it is the welch plugs, that is not as easily detected without taking the carb off with fuel in it and looking at the bottom flange while holding it level.

 

[Cruisers460]

Rochester Quadrajet rebuilt by National carburetors in Jacksonville Fl. Four years old and didn't run it the last two seasons. Talked to them today and they are thinking the float is sticking, Guess i'll be pulling it apart this weekend. I've had flooding carbs in the past, never so bad as to hydro-lock an engine though!