Merc 260 Dangerous Fuel Flooding Issue

[SeaWeedCT]

Hey Guys,

I have dug around in the forums and have learned as much I can about individual problems now I need some advice on the problem as a whole. My '86 Merc 260 5.7L with Rochester Quad is dangerously flooding out the accelerator pump and through the gaskets onto the manifold, I'm afraid eventually it will ignite while I'm working on it because there is soooo much fuel leaking out. The boat runs great and healthy until it gets warmed up then it starts to die out and flood like crazy. Even after the motor dies fuel is still POURING out into the primaries and you can see fuel vapor when you open the butterflies. This year I have cleaned the distributor (new internals) w/ cap & rotor, new NGK plugs (which are now black as can be, meaning it's running EXTREMELY rich), new Quicksilver mechanical fuel pump, fresh gasoline with startron and carb filter and water sep fuel filter, new fuel lines from the tank to the pump, new anti-siphon valve, fresh oil / filter, and rebuilt TWO different quadra-jets twice each, and still the problem persists. I'm contemplating buying either the Holley 4175 or Edelbrock 1409 just to see if the carb is problem and I suck at rebuilding quadra-jets. I'm 100% sure the float level is adjusted right, I've checked it over 10 times, 1/4" from the top, needle and seat have been changed twice as well and the float. Is it possible that the fuel pump is over pressurizing and raising the fuel pressure too high so it blows past the needle in the carb??? The fuel pump is new and I've never heard of that happening; if so what tool do I use to test the fuel pressure, I've only tested fuel pressure on outboards and that will definitely not work here on these steel lines. Could this also be a different problem, I'm stuck, thanks for the help

-Al

 

[Bt Doctur]

Re: Merc 260 Dangerous Fuel Flooding Issue

check the float, could be gas soaked or if hollow ,filling with gas.

 

[SeaWeedCT]

Re: Merc 260 Dangerous Fuel Flooding Issue

check the float, could be gas soaked or if hollow ,filling with gas.

Float is new, basically everything in the carb is new. I disassembed it, soaked everything in cleaner for 24 hours then blew it out with compressed air, then reassembled using the OEM manual.

 

[rodbolt]

Re: Merc 260 Dangerous Fuel Flooding Issue

yes its possible your fuel pump has to much pressure.
I replaced one last year on a 3.0L and the carb flooded after the quicksilver pump was installed.
it was putting out 50 PSI.
carb needle could not stop the fuel.
pressure should be between about 5 and 7.5 PSI.

 

[6meter]

Re: Merc 260 Dangerous Fuel Flooding Issue

No offense meant, but you said you're not good with Q-jets. The needle and seat is not stopping the gas flow. Either the pump is way to strong or more than likely a bad needle and seat. Delco kits should only be used. Aftermarket kits, as in Standard, don't make them well, from experience.

 

[missalot]

Re: Merc 260 Dangerous Fuel Flooding Issue

I fought a Q-jet for a time that would every now and then flood all over the place. After spending a couple hours on the work bench, I found that at certain angles the float would STICK. The "forks" where the pin that the float pivots on was worn a little wide, a little bending and it has been fine for 7 years.

Good luck.