Fellow do-it-yourselfers,
I am posting this because I wish I could have found a post like this instead of struggling along and spending more time and money. This post is intended for folks that have recently installed a new mechanical fuel pump and now find themselves fighting a flooding problem. I think the remedy only applies to a specific set of Mercury engine model(s) but I can only attest to the fact that my 1997 Mercury 3.0LX A1 s/n OK018438 has this peculiarity.
The symptom is an engine that will not idle and will die coughing up fuel through the carb throat and then proceeding to drip fuel into the intake for a few minutes. The typical advice I found on multiple boating forums is to rebuild the carb (in my case a Mercarb 2BBL) and or to replace the float needle with the new spring version. That exercise was very informative and not difficult to do by following the instructions. However, that did not solve the problem.
What solved my problem was to replace a resin-based "shim" between the recently installed fuel pump and the engine in addition to the normal gasket. This shim was not mentioned or included in the manual or parts drawings that I was able to find. It was, however, installed at the factory and unwittingly left out by me when I replaced the pump at the end of last boating season. Thank god I saved it because the Mercury mechanics I talked with had no clue what I was talking about when I called them to ask about what it was and if it were required.
Apparently the lever that is inserted into the crank housing protrudes too far into it and the lobe that contacts the lever to operate the pump displaces it to far causing the pump to output the fuel at a pressure to high for the carb overcoming the float needle which then remains open even when the bowl is filled to its maximum capacity. This dumps fuel into the carb throat. The shim reduces the amount that the pump level extends into the engine and reducing the lever action and output fuel pressure to an acceptable psi level.
Another thing worth mention is that the gasket pattern for the fuel pump and the shim are not the same. The shim seems to match up well with the engine but not the pump or pump gasket. The bolt holes line up fine and this mismatch is apparently normal. Make sure you use a gasket sealant.
Happy boating season from Woodinville!!
I am posting this because I wish I could have found a post like this instead of struggling along and spending more time and money. This post is intended for folks that have recently installed a new mechanical fuel pump and now find themselves fighting a flooding problem. I think the remedy only applies to a specific set of Mercury engine model(s) but I can only attest to the fact that my 1997 Mercury 3.0LX A1 s/n OK018438 has this peculiarity.
The symptom is an engine that will not idle and will die coughing up fuel through the carb throat and then proceeding to drip fuel into the intake for a few minutes. The typical advice I found on multiple boating forums is to rebuild the carb (in my case a Mercarb 2BBL) and or to replace the float needle with the new spring version. That exercise was very informative and not difficult to do by following the instructions. However, that did not solve the problem.
What solved my problem was to replace a resin-based "shim" between the recently installed fuel pump and the engine in addition to the normal gasket. This shim was not mentioned or included in the manual or parts drawings that I was able to find. It was, however, installed at the factory and unwittingly left out by me when I replaced the pump at the end of last boating season. Thank god I saved it because the Mercury mechanics I talked with had no clue what I was talking about when I called them to ask about what it was and if it were required.
Apparently the lever that is inserted into the crank housing protrudes too far into it and the lobe that contacts the lever to operate the pump displaces it to far causing the pump to output the fuel at a pressure to high for the carb overcoming the float needle which then remains open even when the bowl is filled to its maximum capacity. This dumps fuel into the carb throat. The shim reduces the amount that the pump level extends into the engine and reducing the lever action and output fuel pressure to an acceptable psi level.
Another thing worth mention is that the gasket pattern for the fuel pump and the shim are not the same. The shim seems to match up well with the engine but not the pump or pump gasket. The bolt holes line up fine and this mismatch is apparently normal. Make sure you use a gasket sealant.
Happy boating season from Woodinville!!