Mercruiser 350 MPI dies at quick throttle down.

[chambers1517]

I have a 350 MPI and if i am running on plane and pull the throttle back to idle fast the engine dies. It will then not turn over. It acts like the timing is off. After about a minute it will start and run fine. The engine idles fine and doesn't stumble on takeoff. It just dies at fast deceleration? Any ideas?

 

[alldodge]

I have a 350 MPI and if i am running on plane and pull the throttle back to idle fast the engine dies. It will then not turn over. It acts like the timing is off. After about a minute it will start and run fine. The engine idles fine and doesn't stumble on takeoff. It just dies at fast deceleration? Any ideas?

I would suggest checking your exhaust flappers, you might be getting water into the exhaust valves from back wash. Might be real close to hydro lock

 

[Bt Doctur]

It does sound like a bit of hydrolock if it wont turn over. , but why are you doing such a thing.?

 

[chambers1517]

I'm not doing g anything. I'm just pulling the throttle back to stop. It is still in gear since I have the dual controls but it shouldn't kill the engine.

 

[alldodge]

Agree it should not kill the engine, but if water is rushing past the flappers it could kill the engine

 

[JoLin]

I'm not doing g anything. I'm just pulling the throttle back to stop. It is still in gear since I have the dual controls but it shouldn't kill the engine.

You said that you're pulling it back to idle 'fast.' It just isn't a good way to operate a boat. Rapid deceleration causes a sudden increase in engine vacuum which can, as others have noted, pull water through the flappers and into the cylinders.