I have a 1981 15HP Evinrude that runs for 20 seconds and then quits. A couple days ago I did not have problems with the motor. Now….it takes several pulls to start (blister on the hand) and finally starts. (I do have new spark plugs) I can go full speed on the water for about 20 seconds or so. The bulb is hard – I bought a brand new OMC Evinrude/Johnson hose, bulb and connectors. I have new 50:1 gas in the gas tank. What to do next???? Very Frustrated!!!