My 2002 mercury 4 stroke 40 hp Bigfoot was stalling at 2000 rpm. The primer bulb is caved in. If I can get it passed 2000 rpm it runs fine, but when I slow down, it stalls. I have checked the pick up, changed the fuel filter, spark plugs, checked blockage on gas tank vent. I brought a friend over and he noticed gas coming out of the exhaust. Could it be a bad coil? Checked all the spark plugs and they are firing. The problem has progressively become worse. The boat starts up and sounds fine, but after a minute of idling, the motor sounds like it is starving of gas, even though it is coming out of the exhaust. Any suggestions would be great.