The saga continues...

Beefer

Lieutenant Commander
Joined
Aug 4, 2008
Messages
1,737
Ok, quick recap;

1984 Merc 488 bogs down after some time, and will most often times stall. This can be at WOT, or 1/2 throttle, or even just over idle (around 1500rpm).

I've changed a bunch of stuff (including all the fuel), all fuel system filters are new, gave it a tune up, new coil, and (yesterday) 'polished' the fuel.

So today, we're running home from a storm that blew in faster then I (and every one else at the island) anticipated, and she starts bogging down and stalls about 5 minutes into running. On the way to the island, no problems. While I'm sitting there, I check the fuel water separator, and some water comes out. I noticed yesterday there seems to be quite a bit of condensation getting into the tank from somewhere (most likely the vent). Heck, it's Florida, humidity capital, so I'm not panicked about it. FYI, have about 1/3 tank (of an 80 gal tank). After I checked/emptied the fws, she starts up, and I head back towards home.

Again, all is fine for about 10 minutes, and she bogs down again, and dies. Grrr. So I check the FWS again, but this time, instead of water or gas coming out, AIR got sucked in (or out, couldn't really tell). Aha you say! Fuel vent is clogged. Nope.....I can blow through it with little effort. Anti-siphon valve is stuck? Nope, just replaced it this morning as a precaution. Crud in the tank? Doubt it. I siphoned the fuel through 2 filters and back into the tank yesterday for 3 hours (that was fun). No screen on the pick-up tube, so that's not it.

Fuel system schematic is as follows; fuel filler neck/cap (brand new), old fuel fill rubber hose (1 5/8"(?)), aluminum in floor tank (original), fuel pick-up (aluminum), new anti-siphon, 2-3' of *newer* (looking) 3/8" rubber fuel hose, fuel water separator (filter 3 weeks old), same *newer* 3/8" rubber fuel hose to fuel pump filter (3 weeks old), to fuel pump (assumed original), remaining fuel lines are steel. Filter at carb is also 3 weeks old. Rochester 4bbl (rebuilt 2 yrs ago).

Fuel tank vent at thru-hull was corroded, and is now broken, and tank vents into cockpit area in a water and weather-protected area (but open air so fumes don't accumulate). I'll be replacing the vent thru-hull fitting as soon as the one I ordered gets here, so don't beat me up about that. :redface:

Any ideas?
 

EddiePetty

Lieutenant Junior Grade
Joined
Aug 25, 2008
Messages
1,008
Re: The saga continues...

...have you checked the fuel pump itself? Kinda sounds like it's puking fuel thru the tell-tale and alternately suckin' wind.

Try a pressure/ vacuum test on the fuel pump.
 

Beefer

Lieutenant Commander
Joined
Aug 4, 2008
Messages
1,737
Re: The saga continues...

If the vacuum is being created before the pump, wouldn't that indicate that the pump is pulling? I'm thinking there is a restriction somewhere, but just not sure where to look.
 

EddiePetty

Lieutenant Junior Grade
Joined
Aug 25, 2008
Messages
1,008
Re: The saga continues...

...you're missing the point of my previous post....re-read it real slow.

At the least, do the pressure/vacuum tests to rule out the fuel pump :)
 
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