Join Date: Jun 2012
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Re: 1981 Evinrude 9.9hp 2str starts but won't run
The fuel pump fills the carb bowl, but vacuum thru piston operation draws it into the reeds. Thus I'm thinking if it's the fuel pump would take more than a few seconds to empty the carb bowl . It should continue running if you pump the hose bulb even if fuel pump is bad. Since it's running initially continue to focus on the fuel system. The hose is often suspect as there are orings that leak, check valves that stick, or crack in the hose or bulb. The fuel delivery to the carb is suspect, if when the engine falters a quick shot of starting fluid will carry it a few more seconds.
Take the spark plug out right after it shuts down and see is it dry? On mine, that revealed tiny water drops on the piston which were from leaking by the head gasket. No other symptom other than I could start it but wouldn't keep it running. It also occurred right after replacing water pump so maybe the higher pressure brought on the water leak. This isn't perfect troubleshooting but maybe will keep you going today.
The engine speed below the point of cam roller moving the butterfly is controlled by rotation of the magneto plate which advances the spark timing.
Last edited by Sea Dawg; 08-13-2012 at 12:43 PM.