Re: 2 stroke fuel system explanation?
On the 25 merc, 2-stroke the pulse hole in the gasket creates suction to pulsate the fuel pump that is built into the side of the carb. If the gasket is mounted wrong the only way its going to stay running is keep spraying gas into the carb.
When you pull the primer it pushes on a plunger on the opposite side of the carb of the fuel pump. Sprays a little gas in the intake manifold and aids in starting. Once it starts the vaccum caused by the piston stroke runs through the front of the carb through the pulse hole and pulls on the fuel pump diaphram causing it to pulsate and creates a fuel flow into the carb, and into the engine while it runs. While it's at idle, the fuel flow is directed past the idle speed screw on the front, top of the carb...therefore that screw has to be set right to keep it running (about 1 1/4 turn from lightly seated), adjust it in water, in forward gear...idle. When you hit the gas, at about 1,200 RPM's the fuel flow is then pulled from the bottom of the carb through the highspeed jet that is placed in that brass screw in the bottom of your float bowl, bypassing the idle speed screw and taking it out of the equasion while at WOT. When you let off the gas and return to idle the fuel flow is then directed back through the idle speed jet and thats why when you let off the gas, the motor RPM's are a little erratic for about a minute into idle.
To the best of my knowledge this is how this carb works. If I'm wrong someone please correct me.
