The Ongoing Carb Saga...

[sdemore]

I've been running the engine at least every weekend, to keep things from getting gummed up or creating other problems. After the fuel pump valves stuck, somebody recommended shutting off the fuel and letting the engine burn off whatever is in the lines during shutdown. I did that last weekend (**NOTE: an A4 will run for quite a while before the lines and filter are empty**).

We had a beautiful weekend, so I went down first thing this morning, opened the boat up, took off the sail covers, and got everything ready to go. Turned on the fuel valve and the engine fired right up, ran for about 30 seconds, and died. Tried several times, but it wouldn't start again.

I ran home, grabbed my spare carburetor, cleaned it because I didn't do that with the last change, a few months ago, and swapped them out. During the swap, when I removed the scavenge tube, about a cup of gas came out of the carburetor throat. I'm not sure whether shutting off the fuel and draining it caused the float valve to stick open or what, but I don't understand how that much fuel would have made its way into the throat in 30 seconds of running.

[joe_db]

First thing - what is the gas like?
If it is goopy varnish crap-gas, it will stick the float open and/or closed.
Second thing - what does the carb look like? Is the float chamber clean? Does the needle valve move freely? Does it have the dreaded white powder corrosion?

Here is how it works on my boat: When I come into the slip and put the stern lines on, I leave the engine running at idle in forward and shut the fuel pump off. The fuel pressure falls to zero pretty quick - 30 seconds maybe - and the engine continues to run for at least 2 or 3 minutes or more while I am up on deck getting the rest of the lines on.

Starting I turn the ignition on and hold the prime button. The fuel pressure jumps around a bit on the way from 0 to 4 and when it holds steady on 4 I start the engine. I have no issue with the float sticking on or off since I got a new carb. The old one was suffering the corrosion and endless issues.

[sdemore]

This was a carb that I sent out last year for a rebuild. It was a disaster of an experience, but that is a different story. The carb took over a year to come back, so has only been in the boat for 3 or 4 months. I haven't disassembled it yet, but when I drained the bowl and throat, there was a bunch of black crud in the gas I collected. The black paint this guy used to paint the carb was dissolving, so I assume that is what the crud was.

While the carb was off, I pumped the fuel pump several times and collected a couple of cups of gas. There was nothing visible in it, but that doesn't mean it isn't goopy or varnished. When I picked up the boat last year, it had been sitting on a mooring ball for 3 years (no engine in it) and the fuel tank was bone dry without any sign of rust or dirt (it is a monel tank). I replaced the sender before adding any gas, so it should have stayed pretty clean. I think the bulk of the problem is the rebuilder of the carb and the piss poor job he did. The previous carb (my spare) I rebuilt and it did great, until I had a couple of sticking intake valves that allowed this tar looking stuff to come back through the manifold and into the carb.

The gas is all fresh, but I'm not convinced that there isn't something getting into it from the lines or the water seperator. I suspect everything was dry when I got it because of evaporation, not because of cleanliness.

[CalebD]

Sometimes a gentle tapping on the carb with a screw driver handle can cajole the float needle to move.

Also draining the main passage plug on the carb helps I find. Air needs to get in there where fuel collects.

Carb maintenance.

[joe_db]

Did the INSIDE of the carb get painted
* at some point, paying Moyer for a new carb can be the best money you will spend

[sdemore]

I haven't pulled the carb apart yet, but as bad as this guy was, I still can't imagine he painted the inside. Overspray maybe... I suspect the paint came from the outside of the carb, as I was draining out the fuel in the bowl and the throat.

The backup carb is Moyer rebuild. A guy bought it as a spare and it sat for several years, still in the box. It worked great until the intake valves stuck open and loaded it with a tarry crud. I cleaned it (again) and it is back on now and working great.

My original confusion still exists though. If the float valve is the culprit, can it allow enough fuel to go by to fill the throat of the carburetor?

[joe_db]

I haven't pulled the carb apart yet, but as bad as this guy was, I still can't imagine he painted the inside. Overspray maybe... I suspect the paint came from the outside of the carb, as I was draining out the fuel in the bowl and the throat.

The backup carb is Moyer rebuild. A guy bought it as a spare and it sat for several years, still in the box. It worked great until the intake valves stuck open and loaded it with a tarry crud. I cleaned it (again) and it is back on now and working great.

My original confusion still exists though. If the float valve is the culprit, can it allow enough fuel to go by to fill the throat of the carburetor?

Yes it can!

[tenders]

Yes it can!

Yes, if the needle valve gets stuck in the "down" position (perhaps the float is mired in a bit of goo from vestigial fuel evaporate), or if there is a bit of dirt or worn-off rubbery coating preventing the needly part from making the seal, the fuel pump will happily fill the float chamber and keep squirting fuel around the tip of the disengaged needle valve and into the carb throat.

That's why tapping the carb can help dislodge the needle valve. I *think* some Seafoam in the fuel will also help dissolve the sludge, but it isn't clear it does this more any efficiently than just regular old clean fuel.

[indigo]

If the rebuild was as poor as you indicate, the rebuilder may have removed the needle valve seat and replaced the seat using the same gasket that was there originally. I have had that same experience and it turns out those gaskets are “one time use”. Putting the seat in with the used gasket can result in a very big leak around the needle valve similar to what you’re experiencing.
Experience is a wonderful teacher!