Leaky Diaphragm?

[MikeT]

When I changed my oil this year it smelled a little like gas. (The boat is new to me so I don't know if this has been on-going) Watching it siphon from the oil pan, it looked dark and thick until the very end when it thinned to a water-like consistency for a few seconds before the siphon stopped. I took the used oil to my mechanic and asked him if he thought there was gas in it. He felt the oil did not have a strong gas odor and it was most likely caused by "blow by from the carb". The Moyer Marine site indicates that the gas smell could be caused by a leaky diaphragm in the mechanical fuel pump. Since this is a potentially dangerous situaution what is the best course of action? Is it likely that the thin running liquid at the end of the siphon was gas or could it have been water? Will used oil naturally have a some gas smell?

[Don Moyer]

Mike,

Mike,

You might have a potentially dangerous condition, if gas is in fact getting into your crankcase through your fuel pump. Your symptoms are very consistent with this being the case.

You can check your fuel pump by disconnecting the line between it and the carburetor, and then reattaching the line to the pump. This will give you a convenient spout from which to pump fuel into a jar.

After establishing that the pump has a good flow, hold your finger over the end of the fuel line, and work the priming lever one or two more times to pressurize the line against your finger. If the diaphragm is OK, the pump should hold pressure against your finger for a minimum of 30 to 45 seconds.
If the pressure bleeds off quickly from the fuel line, the diaphragm is no doubt leaking.

[MikeT]

Don, if it is the diaphragm how do I repair it? I see the MMI site sells rebuild kits but I did not see the diaphragm itself. Does the repair require a complete rebuild? If so, how difficult is it? Should I just replace it or consider upgrading to the Facet electric fuel pump mentioned in the MMI service manual?

[Don Moyer]

Mike,

Our fuel pump rebuild kits do include a diaphragm, and there is a set of instructions included with each kit. In terms of difficulty, I guess I'd rate rebuilding of the mechanical fuel pump on par with removing and replacing the distributor for repair.

Our customer base is divided almost straight down the middle in terms of personal preference regarding fuel pumps. We consider the mechanical pumps to be very a reliable option, and our current line of electrical pumps are also extremely reliable, all of which makes choosing rather difficult. We have no data to suggest that one type of pump has any benefit over the other in terms of life expectancy.

Best regards,

Don Moyer