1998 johnson 40 hp won't idle when tank is 1/2 full and less

[sgfrye]

40 hp johnson won't idle when tank is less than half full.
any thoughts would be greatly appreciated.

couple months ago my wife and i bought a pontoon with a 1998 johnson 40hp

we have had it out on the lake 5 times now.

it runs great from idle thru wide open throttle when the gas tank is full down to about a half tank.

after the tank is half full or less it runs great above idle but does not idle good, keeps cutting off then is hard to restart.

here is what i know about the engine's history

2 months ago the carbs were rebuilt and adjusted
new plugs
new fuel pump
new fuel line and primer bulb
new fuel filter

tank is 12 gallons, vent is open
fresh gas
seafoam was added to my last tank of gas.

idle speed seems ok
compression hasn't been checked

many thanks

[boats.net]

If you keep it running by pumping fuel primer bulb then it could be fuel pump, fuel hose, tank vent or pickup tube in gas tank. If pumping primer doesn't keep it running then problem is at engine, dirty carbs, intake gasket leaks, compression problem.

[Joe Reeves]

Check the pickup line inside the tank. Sounds like it has a pin hole around the halfway mark.... draws air.