Carburetor Flooding

[mingamells]

I have had intermittent flooding problems for over 10 years and cannot figure it out. By flooding I mean the engine dying and fuel pouring out of the carburetor. Based on past advice from the old sailnet forum, I suspected the needle valve was not closing, so I measured the fuel pressure, which was (and still is) 5.5 psi. My understanding is that this is too high. I bought a new fuel pump when I bought the boat (about 11 years ago), and suspect the pump is not suitable for an A4. Along the way, I have rebuilt the carburetor 3 times and bought a new one (about 4 years ago). I have a 25 main jet, and 12 idle jet. About 2 years ago, I installed a fuel pressure regulator (designed for hotrods) and reduced the fuel pressure to about 2 psi. The frequency of flooding seems to have decreased, but still occurs. AS it is, the engine is unreliable and unsafe. Due to repeated engine failure, I have had to sail into a downwind slip by myself so may times, luckily without any boat damage. A related observation, is that when I listen to the carburetor air inlet while the engine is running, I hear "slurping", like raw fuel is sucked into the throat. Generally, when the engine floods, I disassemble the carburetor, put it back together, and generally it will run again. I like the A4 generally, but I need to be able to rely on the engine.

Does anyone have any troubleshooting advice? I am thinking of replacing the fuel pump, but maybe that is not the problem.

Thanks in advance.

[Don Moyer]

Hello,

The sound you're hearing from the intake of your carburetor is interesting. I never heard of a "slurping" sound being reported before, but almost any sound that anyone would recognize as unusual from the intake of the carburetor relates to a blockage within the exhaust system. If the exhaust is partially blocked, acceleration will also be very sluggish. The most common description is that of a "gagging" sound.

If there is a blockage in the exhaust system, a gagging sound will normally be accompanied by droplets of fuel flying out of the carburetor if you try to accelerate the engine.

In another direction entirely, something as simple as dirty fuel can cause a carburetor to flood by preventing the needle and seat of the float valve to fully close. If you haven't already done so, you should install a good primary fuel filter with a water separator and a small inline filter between the fuel pump and carburetor. The primary filter typically has a 10 micron mesh, and the inline filter will usually have a 1 micron mesh.

It does not sound like there is anything seriously wrong with the engine itself.

Best regards,

Don Moyer

[mingamells]

Thanks Don.
I replaced the exhaust system recently, and I have a similar fuel filtering system to what you recommend. Is it possible, the carb. is getting more fuel than it can atomize, due to high fuel pressure? The "slurping" sound seems to be large droplets of fuel sucked in by intake vaccum. Its like the sound you make when you suck on a straw from a drink thats almost empty. It doesn't make this sound at idle, except when its about to flood, when it won't run below 1200 rpm and misses at all speeds. Do you think a new electric fuel pump would be worth a try?

[Don Moyer]

Hello again,

I don't think that you'd gain anything by replacing your fuel pump as long as you trust your pressure reduction relay. In your last report you indicated that you were regulating the pressure to 2 psi which should have no potential for forcing past the float valve.

In re-reading your first report I notice that you have a main jet with an index number of 25. You didn't mention whether you have an early model or late model engine, but a main jet with an index number of 25 would only be used in an adjustable main jet. The correct index number for a late model fixed main jet is 21 which would have a considerably smaller orifice. If you are using the 25 index as a fixed main jet, this would certainly explain your rich condition.

Don