[bird203]

I have a carburated 1996 225 mariner. There is an inline racor filter and an installed glass final fuel filter on the engine block. My problem is when the engine is shut down, oil from the injection oil tank backs up thru my fuel lines and fills the racor filter with 2 cycle oil. This fouls the plugs as soon as you try and start the engine. Someone told me it could be backing up thru the oil pump on the engine but to do that it would need to travel past the check valves in the priming bulb which are good. All three carbs have been rebuilt by my dealer to correct this problem but no good. What to do next?

[rodbolt]

rebuilding carbs wont correct an oil sytem problem. two comepletly seperate subsystems. replace the check valve at the fuel pump and the pressure tap check valve on the lower stbd side of the cranckcase and your problem will dissapear.you really really need to have a dealer that can put a bit more thought behind how the system works or ya need to do a bit of reading yourself. as far as the checkvalves in the fuel primer goes fuel will flow both ways at a low volume or pressure. its either that or release the pressure from the remote tank at each shutdown.

[bird203]

Thanks for the help. I found the problem yesterday. My dealer rebuilt the fuel pump and had installed a gaket upsidown which tore the gasket stopping full fuel flow from one cylinders pulse. Oil was still moving from the oil injection pump with no fuel to go along with it, starving the engine and fowling the plugs. Since the engine oil tank retains about 2psi for some time after shutdown, the oil would leak by the damaged gasket and fill the fuel line. Easy fix once I decided my dealer had no clue and I broke out the book.