Is the electric fuel pump supposed to be able to aspirate/suck gas thru a dry line?

**rigspelt** · 06-29-2009, 06:05 AM

What about the tank air vent line? Could it be blocked?

My read of the forums is that electric fuel pumps can sometimes prime empty fuel lines on A4s. It worked in our boat this spring after installing a new pump and new fuel lines with two new inline filters, once we remembered to open the fuel shutoff valve.

When I installed the new carb on the weekend, the engine started in about 10 seconds (several burps of a few seconds), so the pump primed the partially dried line and new empty carb. Not sure if we are just lucky to have the right gravity assist in our setup. I had elected not to install a hand-squeeze pump inline.

**Don Moyer** · 06-29-2009, 07:06 AM

Dick,

An electric fuel pump might prime successfully if the fuel supply system has very little head loss built into it on the suction side of the pump, or where the fuel level in the tank is above the engine. However, if there is any restriction at all on the suction side of the pump (like your spring loaded check valve) an electric pump will frequently not prime itself and will need to be artificially supplied with fuel to start operating. Mechanical pumps are a bit more forgiving, but they too will sometimes have a problem moving air through and out of the fuel system. Fuel pumps are simply not good air compressors.

In my view, spring loaded anti-siphon valves should be avoided in favor of a manual fuel shut-off valve. While the pump might work successfully for years with this additional head loss on the suction side, in the heat of the summer when the vapor pressure of gasoline can get quite high, enough gas can evolve out of the fuel to create an air bubble in the lines leading to the pump, which might account for some of the unexplained shut-downs we experience each season.

Don

**dvd** · 06-29-2009, 11:53 AM

My read on the electric fuel pump vs. manuel is that the electric tends to worry me. My A-4 has a manuel fuel pump and from what I have heard I believe it is the safest set up. I have heard that the electric fuel pump can overcome the check valve in the carbuerator and start pumping fuel into the bilge. (not good) And from what Don just said about "fuel pumps not being good air compressors" I don't really see an advantage over the stock manual pump. I was considering an electric fuel but if they aren't any better at purging the system of air than the manual I think I will stick with a manual pump even if I need to replace it at some point. I wonder how Don feels about this issue and he has any recommendations.

DVD

**DickBennett** · 06-29-2009, 06:46 PM

Thanks all,
I will replace the nipple that has the anti-sipon check valve in it with a straight through, prime the fuel line and make sure there is a vent (which unless it is part of the gas cap up on the deck, I don't think there is one!!!). That should do it. If it works, I will put off deciding to switch to a manual fuel pump until a later date.
Thanks so much!
/D

Originally posted by dvd View Post

My read on the electric fuel pump vs. manuel is that the electric tends to worry me. My A-4 has a manuel fuel pump and from what I have heard I believe it is the safest set up. I have heard that the electric fuel pump can overcome the check valve in the carbuerator and start pumping fuel into the bilge. (not good) And from what Don just said about "fuel pumps not being good air compressors" I don't really see an advantage over the stock manual pump. I was considering an electric fuel but if they aren't any better at purging the system of air than the manual I think I will stick with a manual pump even if I need to replace it at some point. I wonder how Don feels about this issue and he has any recommendations.

DVD

**msauntry** · 06-29-2009, 07:38 PM

I believe Don's engines are supplied with an electric fuel pump. If the gasket fails on the mechanical pump, you can end up with gas in your engine oil which could ignite inside the block and do some damage, or at the least it will thin out your oil and cause damage from lack of lubrication. But until then, it works fine. Change your gasket if you haven't done so yet and it'll give you plenty of trouble free service I'm sure. Like most things, a little bit of preventive maintenance can save a lot of money and trouble.

**keelcooler** · 06-30-2009, 01:19 PM

The wrong electric fuel pump or an improperly wired up pump could lead to disaster. At over 4psi fuel could overcome the carb float valve causing flooding. A by passed oil safety switch has caused many fires as reported on this forum. Same story,engine stalls,key left on,raw fuel flowing out of carb intake finds ignition source or hot surface. The manual pump can only deliver fuel when the motor is turning.

**DickBennett** · 06-30-2009, 07:40 PM

Thanks! That is great info to have! I'll start studying how difficult it is to switch to a mechanical pump.
/D

**msauntry** · 07-01-2009, 10:54 PM

If the electric pump is properly wired to the oil pressure safety switch then it won't supply fuel except when the engine runs, just like the mechanical pump. If you can't tell if its wired correctly, then you might be better off with a mech pump.
My boat was wired incorrectly when I bought it and it was quite a while before I figured out the proper way.

Some boats with gas tanks below the engine need a little more pump psi (certain Catalinas) than other boats that have it even or above the engine. I think both pumps are reliable and safe, though.

**keelcooler** · 07-02-2009, 08:07 AM

If you turn on your key and the pump starts clicking it's without a safety switch. Time to install one asap. No reason to switch to a manual pump if your 12vt is working properly. Just make sure it's approved for marine use and is rated under 4psi. Your fuel feed hose once primed and attached to the pump should provide good flow to the carb. If you then have a flow problem or air bubbles you still have a fault up stream. Check all attachments including removal of the pick up tube in the tank. If it flows good only with the fuel fill cap off you have a plugged vent.

**DickBennett** · 07-06-2009, 02:11 PM

Thanks you,
I found the vent at the top starboard corner of the stern. Just a fitting with two permanent holes (no open/close vent valve) and a line to the back of the tank separate from the gas fill line. Looks o.k.
I used a punch to knock the anti-siphon valve out of the nipple on top of the gas tank and primed the fuel line. Still no gas getting to carb. I took off the fuel pump and tested it in my garage with a short (12 inch fuel line into a bucket of gas and 12v battery. Works just fine. I took off the carb and opened it up, per the instructions in the manual. What mess! Thick white paste (like toothpaste) in the bowl and all over the floats and jets.
I am ordering a new carb. now. I have pictures of the inside of the carb. if anyone wants me to post them, but take my word for it, it is just a mess.

/D

**sastanley** · 07-06-2009, 02:24 PM

Of course we want pictures!!

**roadnsky** · 07-06-2009, 03:16 PM

Originally posted by DickBennett View Post

I have pictures of the inside of the carb. if anyone wants me to post them, but take my word for it, it is just a mess.

We love pics! And messes (especially carbs) are great learning experiences...

**DickBennett** · 07-06-2009, 09:22 PM

O.K. , here they are, but viewer discretion is advised, these images may be disturbing to sensitive stomachs.
B.T.W., When I first opened the carb. the white stuff was wetter, more jelly like. By the next morning when we took these pictures it was pretty much dried down to a more flaky, crusty appearance.

Also, I do know that if I was any kind of a mechanic or had an once of courage, I would just clean all the jets and parts in BrakeClean or Carburator Cleaner, gas and forced air; buy a few cheap gaskets and put it all back together. But let's face it I'm just a wimp. I bought a new carb.
/D

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