Mechanical Fuel Pump: Diaphragm issue

[Clucas]

Experienced what seemed like a fuel-related shutdown this weekend an started trouble shooting. After some cranking (yes, thru-hull was closed ), I removed the flame arrester from the carb expecting to see some fuel puddled -- bone dry. Operating the priming bail on the fuel pump, I could hear fuel moving, but when I removed the main passage plug on the carb, it was dry. Replaced the plug, moved the the priming bail and gave it another shot -- started this time, but needed to keep rpms high -- figured I might be moving some crud through... Same thing again on Sunday. Removed the fuel pump this morning and found pieces the diaphragm coming off (and I'm sure ending up in the carb). Anyone seen this before (see pic)? Ethanol related? I just replaced the diaphragm 2 years ago.

Cleaned it all up, brought home the carb, tore it down and cleaned it with carb cleaner and compressed air. Hopefully case closed, but I was very surprised to find the debris I found (it was all from the textured center section of the diaphragm).

[dvd]

I think the rubber corrosion is somewhat normal. This is why you must have a polishing filter BETWEEN the pump and the carb. If you have a polishing fiter maybe it has done its job and is now clogged.

dvd

[ndutton]

Now would be a good time to check the oil level for overfill and sniff it for gasoline fumes. Just sayin' . . .

[marthur]

I just replaced the diaphragm 2 years ago.

My first diaphram lasted 30 years and the second is approaching 10 years without shedding rubber like that. Where did you source the part?

[Clucas]

My first diaphram lasted 30 years and the second is approaching 10 years without shedding rubber like that. Where did you source the part?

Part is from here as part of a mechanical pump rebuild kit (Product No. - FPMP_13_320).

[Clucas]

I think the rubber corrosion is somewhat normal. This is why you must have a polishing filter BETWEEN the pump and the carb. If you have a polishing fiter maybe it has done its job and is now clogged.

dvd

I have a polishing filter in place and just replaced it in April of this year (I write the date on them as I do my Racor). Hard to believe it's clogged given that the I've put maybe an hour on the engine so far this season.

[Clucas]

Now would be a good time to check the oil level for overfill and sniff it for gasoline fumes. Just sayin' . . .

Thank you, Neal -- will certainly check. At the risk of sounding like a complete moron, how could/would I end up with fuel in my oil? What am I missing?

Chris

[ndutton]

Sorry Chris, I figured I'd harped on it enough that . . .

The USCG has a specific requirement for diaphragm type fuel pumps for inboard gasoline engines that they do not leak fuel in the event of diaphragm failure. The way the requirement is met is to deliver errant fuel into the engine's crankcase thereby keeping it contained and not in the bilge. The two things I mentioned (elevated oil level and gasoline smell) are indicative of a breached fuel pump diaphragm.

edit:
I can't say if fuel was dumped into the crankcase but under the circumstances I think it merits checking.

[Clucas]

Sorry Chris, I figured I'd harped on it enough that . . .

The USCG has a specific requirement for diaphragm type fuel pumps for inboard gasoline engines that they do not leak fuel in the event of diaphragm failure. The way the requirement is met is to deliver errant fuel into the engine's crankcase thereby keeping it contained and not in the bilge. The two things I mentioned (elevated oil level and gasoline smell) are indicative of a breached fuel pump diaphragm.

Ah, got it - thanks. No holes or failure in the diaphragm apart from it appearing to be disintegrating (which technically could be considered a failure and yes, I will be replacing it). Good thing it's so easy to get to . Will definitely check oil level and gasoline fumes in the crankcase.

[Dave Neptune]

Bit o' hose

Those look like hose chunks cut out by barbs to me!

Dave Neptune

[Clucas]

Those look like hose chunks cut out by barbs to me!

Dave Neptune

No - they were all loose and coming off the textured center portion of the diaphragm. The largest piece was barely attached -- I rubbed with very little force and what came off is what's in the first photo. In this photo, you can see the rough edges around the perimeter of the textured portion of the diaphragm.

[Dave Neptune]

Hmm

How old is that diaphragm? The diaphragm should not breakdown like that. Are you using any additives? The diaphragm looks like it sat in the sun for a while too.
If it is a very old diaphragm OK but if not what ate away at it? That's what we need to know.

Save Neptune

[Clucas]

How old is that diaphragm? The diaphragm should not breakdown like that. Are you using any additives? The diaphragm looks like it sat in the sun for a while too.
If it is a very old diaphragm OK but if not what ate away at it? That's what we need to know.

Save Neptune

I replaced it no more than two years ago as part of a fuel pump rebuild. The one I replaced seemed to almost be made of a rubber-coated canvas. I'm ordering a replacement today and will talk with Ken to see exactly when I ordered this one. No additives apart from MMO and some Stabil (used over one winter).

[JOHN COOKSON]

Betcha the rubber is not ethanol rated.
I sure would talk to MMI about this.
Maybe soak the replacement diaphragm in a jar of gasoline for a while to see how it performs before you instal it?

TRUE GRIT

[Dave Neptune]

Old style perhaps

The diaphragm for these could sit in a warehouse for years before being sold. If they were built before the E in the gas they should be discarded however not all suppliers are goi8ng to toss them out.

Soaking for a while in gas may be a good check. I doubt the "diaphragm" itself is suspect but the rubber disc under the spring support could well be the offending party.

Dave Neptune