I have a 1979 280E fuel injection it starts good in the morning. and runs great but when I shut it off and leave it set for awhile it will not start like its not getting gas if I take the air breather off and push down on the this flapper cylinder looking thing under the air breather it will start right up how do I fix this problem or what is the problem so that I can take it too a mech. too fix

thnks
jhb