On the advice of a good friend and engine rebuilder for Mercury Marine from 40 years ago, I have not subscribed to the practice of running fuel out of the carburetor at shutdown. His reasoning was running the engine until it was starved of fuel did not run the carb dry, just low enough to spoil the fuel-air mixture needed for the engine to run leaving residual fuel in the carb bowl allowing it to fully evaporate more quickly leaving the nasty residue behind anyway. Sounded reasonable to me so shutting down was a mere flip of the ignition switch leaving a full carb bowl ready for an easy, no-prime start the next time. I admit it was not a popular opinion but it came from a respected source so that was my policy.
Not any more.
My own direct experience last year changed my policy. I now run the carb out when cleaning up the boat after a trip. Following a lengthy layoff I went to the boat for a father-daughter sailing day. I fired up the engine and got busy taking off covers, dock cord, etc. Then the engine quit. Ok, restarted and it quit again. Started it and feathered the choke to try and keep it running but no joy. That was it for the day, I was not about to spend Father's Day working on the engine so we found another way to spend our day together.
The following week I took off the carburetor very carefully, treating it like a land mine and brought it home for a forensic disassembly. The carburetor bowl was empty and the float valve was stuck in its seat shutting off the fuel supply. I keep a rebuild kit on hand so a rebuild was done, carb reinstalled and tested. All good.
I concluded that the long layoff with a full carburetor bowl pressed the rubber tipped float valve into its seat holding it there with float pressure for a prolonged time causing it to stick in place. No way would that have happened with the float valve open so a new shutdown policy was adopted. As a side benefit I now get an EWDS function test at shutdown too. Closing the fuel valve - I have one immediately ahead of the carb - gives me a buzzer and "Fuel" light (low fuel pressure), a minute or so later when the engine stops I get the "Flow" light (low raw water flow) followed shortly by the "Oil" light (low oil pressure).
Not any more.
My own direct experience last year changed my policy. I now run the carb out when cleaning up the boat after a trip. Following a lengthy layoff I went to the boat for a father-daughter sailing day. I fired up the engine and got busy taking off covers, dock cord, etc. Then the engine quit. Ok, restarted and it quit again. Started it and feathered the choke to try and keep it running but no joy. That was it for the day, I was not about to spend Father's Day working on the engine so we found another way to spend our day together.
The following week I took off the carburetor very carefully, treating it like a land mine and brought it home for a forensic disassembly. The carburetor bowl was empty and the float valve was stuck in its seat shutting off the fuel supply. I keep a rebuild kit on hand so a rebuild was done, carb reinstalled and tested. All good.
I concluded that the long layoff with a full carburetor bowl pressed the rubber tipped float valve into its seat holding it there with float pressure for a prolonged time causing it to stick in place. No way would that have happened with the float valve open so a new shutdown policy was adopted. As a side benefit I now get an EWDS function test at shutdown too. Closing the fuel valve - I have one immediately ahead of the carb - gives me a buzzer and "Fuel" light (low fuel pressure), a minute or so later when the engine stops I get the "Flow" light (low raw water flow) followed shortly by the "Oil" light (low oil pressure).
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