Carb float bowl empty after shut down, problem

[manoa matt]

I've been helping a friend diagnose a fuel related problem with her 1978 Fiat spider. Stock 32 ADFA carb.

About two months ago she asked me to do some routine maintenance and replace various hoses belts, water pump and mechanical fuel pump. The rubber hoses in the engine bay including the rubber supply hose from the hard line to the pump and from the pump to the carb were replaced along with the return hose from the carb to the hard line. The car has run great for two months up until a week ago.

She called me to tell me the car would not start. I found that the carb did not have any gas in the float bowl. With the supply disconnected from the carb I held it in a jar while she cranked the engine. No gas came out.

I didn't want to believe it was the new fuel pump I installed two months prior, so I started looking at the rubber hose sections in the supply and return lines. Most were original hoses with visible cracks and deterioration. I replaced the rubber supply and return lines that run along the driver's foot and under the car by the driver's side rear seat pan. After replacing those hoses I checked the flow of the pump while cranking. The pump had great flow and the car idled for about 10 min before she shut it off. She drove the car around the next day and made several stops before returning home. The next day she goes to start the car and same deal.

I come back out and first remove the supply hose at the carb and check the flow while cranking...nothing. I then replace the rubber supply and return lines that go from the pickup at the tank through the trunk up over the axle to the start of the hard lines. These hoses were the worst, and badly deteriorated. After that I rechecked the flow of the pump while cranking and it was very good. Same deal, she drives the car around for a day, makes several stops, returns home, then the next morning it will not start.

At first I thought the pump was sucking air through the deteriorated hose sections, since after I replaced them with new the car would function. However that did not explain how the float bowl was empty each time. I can see how the return line or the supply line could siphon back to the tank, but the float bowl should still be full.

I have not checked the tank vent line or the one way vent valve/flying saucer up above the rear axle. However the last time I left, I told her to leave the gas fill cap loose so the tank can vent and not build up a negative pressure which would siphon back the gas in the supply and return lines. Again, even if that was the case, it should not drain the float bowl. Accelerator pump diaphram is good and the float level was checked two months ago when I replaced the pump.

I'm almost stumped! any suggestions?

Matt

[majicwrench]

Matt,
How do you know the float bowl is emply??
I would not worry too much about the float bowl being empty, the problem, as you are well aware, is that if fails to pump fuel intothe float bowl.
Fuel in the float bowl could evaporate off after shutdown, some could end up in the evap system (if it has one). Again, I wouldn't worry bout it. Fix the problem, fuel fails to pump at times.

Methinks leaving the gaas cap loose is a good start. I had a gas tank on a Firebird collapse once from the vacuum created from using a non-vented cap.

Keith

[manoa matt]

I know the float bowl is empty because I take the top off the carb. That much fuel (in the float bowl) will not evaporate overnight even with a hot engine. I have the exact same car and same setup with no problems.

I believe the pump is functioning properly. Once fuel reaches the pump it keeps pumping strong.

Something is sucking the gas from the supply line and the float bowl after shut off. Apparently it takes a few stop and go trips, but re-occurs within 24 hours after I re-prime the system.

The supply and return lines CAN NOT suck fuel FROM the bowl given their locations at the top. If fuel is leaving the float bowl it HAS to be pushed out through the main and secondary jets.

[joelbert2k]

Matt,
I'm very interested in this problem as I have very nearly the same symptoms with mine.
I have an 80 with an 1800 intake and 32 ADF carb, NOT a 32 ADFA. I have difficulty starting in the mornings and have installed an electric fuel pump to help with that problem. Another, I believe related, problem that I have with this carb is what I feel is a percolation issue. If I drive to a store, say 15 mins away, and park the car while I shop when I come back out the car will not start right away. I have to hold the throttle wide open as if flooded and it will start after some cranking. It then runs badly for a couple minutes until the plugs clear. Not sure what is causing this but I suspect the carb, perhaps it's not venting and is forcing the gas out thru the jets.

Joel

[mbouse]

do either of these cars still have the flying saucer shaped one way valve between the pump and the carb? pitch that thing

[majicwrench]

Matt,
I still think you are chasing ghosts with the empty fuel bowl issue. While it is interesting that the bowl is empty, the pump should be doing itsthing and refiling bowl. Pump should not need to be primed to pump fuel, even if the lines are empty it should pull fuel out of tank all by itself, much like when you run the vehicle out of gas.

I often put a vaccum gauge on the supply side of manual fuel pumps just to see what is happening on that side of things. WIth an engine running, you should see a very slight pulsating vacuum. With engine off, obviously should see all vacuum disappear. Also, you can pinch the supply line at the tank and watch the vacuum with the engine running, should immediatly go way up.
Good luck,
Keith

[Schnauzer]

I had an identical situation with my son's 79 2000. Long story short after going through all the same things you have done I removed the gas tank. The foam pickup filter had completely deteriorated and the tank was full of debris and rust. Cleaned the tank, new pickup screen ( I have the Napa part number for a screen that works) some new line and filters and she works flawlessly.

Hope this helps.

[joelbert2k]

Mike,
I read here that the flying saucer thingie is to be avoided so I removed mine when i put the carb/manifold on.

Keith,
I think the issue with the empty bowl is not so much about the fuel pump needing to be primed but that you have to crank the engine far too long to get fuel back into the bowl. Much too much work for the starter and battery.

Joel

[racydave]

Matt, I wonder if air is getting in? How about capping the lines at the tank and doing a pressure test, or use a hand held vaccum pump and check the integrity? Air is much thinner than fuel...

[manoa matt]

I won't get a chance to further diagnose the issue untill Saturday. Thanks for all the suggestions and keep em comming, they are helping the gears turn to hash out new ideas.

I know of four "flying saucers" or U.F.O.'s (Unidentified Fiat Object)

1. The one way check valve on the fuel return line just after it exits the carb. (I don't suspect this is the problem)

2. The 3 into 1 thingy that's in the tank vent system in the trunk near the fuel filler (some cars have a red/orange metal 3 into 1 flying saucer, while other cars have a 3 into 1 plastic "bar")

3. The flying saucer in the tank vent line that sits above the rear axle. (This is the second saucer in the vent system after the three hoses from the tank merge into one. The line continues out the trunk and up over the axle where this saucer is located.

4. On the 76 I dismantled, it had an electric fuel pump in the trunk. After the hose exits the pump it goes to this flying saucer (check valve) before the line continues to the carb. However the lady's 78, and cars with mechanical fuel pumps do not have this saucer.

I'm thinking if it was any, it would be #2 and #3. I kept both on my 78 when I replaced all the hoses, and apparently both are still working. I did use clear vinyl tubing that runs from the 3 into 1 (#2) to the #3 saucer. On mine there is a clear/amber fluid backed up behind the saucer. I assume either #2 or #3 is a check valve and one is possibly a vapor/fluid seperator.

If someone has pages 38 through 45 from the Fiat 124 parts catalog we should be able to identify the U.F.O.'s My book for some reason is missing those pages.

I have the equipment to apply pressure and/or vacuum to the lines to check for leaks. I also have a gauge that can be used to check the vacuum on the low side of the pump and the pressure on the high side.

I know new pumps can have diaphram problems or melt from the ethenol in the fuel, but I still feel its not the pump. Once I get fuel to the pump and to the bowl the car runs beautifully and never studders or starves for gas while running, even at highway speeds. If I get it started and she drives it around making several stops it works each time. Its only after it sits overnight that the fuel drains out of the lines and float bowl.

I checked the pickup sock in the tank, totally intact and good shape although a bit firm/hard. I did not remove it from the pickup tube for fear of the thing breaking apart or not going back on. If this was broken or the pickup tube blocked then the car would act like it was starving for fuel while running, which its not.

As far as the charcoal canister is concerned, the vacuum tube that goes from the top connection to the vacuum source on the carb is pretty old and brittle. I'll switch this out first. I thought for a minute that the tank was venting to the charcoal canister and since the vacuum hose is probably leaking that it was not drawing off, but that the fuel tank vent line somehow pressurized the float bowl vent line and that is what pushed the fuel out of the bowl through the jets.

However if you ever had your charcoal canister out you will notice if you blow on one of the three fittings while capping off the other two that it is not air tight. Even if you tried to pressurize one of the ports the air will escape through the vent on the bottom of the canister before it pressurizes the other two ports.

[majicwrench]

Matt,
Just wanted to share a story from my days in a Honda dealership 20 some years ago. Civic came in and was hard to start. A little snooping revealed that every time you would shut it down it would empty the fuel bowl. Not overnight, but right away. Hondas had a little window in the float bowl, and you could WATCH the fuel just disappear!! Turns out part of the evap system was full of water, as in cust finally admits that yeah, they did sort of get stuck in a foot of water. There was, and is, no understanding the complexities of a Honda Evap system, but at any rate getting everything dried out fixed the problem.
Not that this relates to what you have going on, but it is a good story.
No idea what flying saucers are on Fiats, but many cars use what they call a pulsator, to smooth out the ups and downs of the fuel pressure, and I have seen some sort of disc shaped on other cars.
Good luck,
Keith

[manoa matt]

Just an update:

Like most problems, it was a combination of several things.

The flying saucer (#3) in the tank vent line was clogged and not letting the tank vent to the vapor canister. It looked like it had been clogged for a while. The hose that connects the tank vent hard line to the vapor canister in the engine bay needed replacement, as well as the vacuum source hose.

The new 2 month old mechanical fuel pump also had a slight problem. The pumps have two small rubber diaphram type one way valves in addition to the pump diaphram. If I blew air through the tank side of the pump it would come out the carb side as it should. If I blow air through the carb side, it should not came out the tank side, but a small amount did. I tried the same test procedure on the old pump (which was the exact same design as the new one) it did not let air back through the pump. I confirmed this again with a third Savara pump.

I reinstalled the old pump and it works fine. She wanted the pump replaced for piece of mind since it was last replaced in 94 and its her daily driver. However she only puts 2000 miles on it each year.

[joelbert2k]

That's very interesting Matt. When I was working under my car I noticed that that valve was disconnected. I merely cleaned it off and reconnected it. I think I shall take a closer look at it now. Thanks
Joel

[manoa matt]

When I was restoring my current spider I remember removing that valve while replacing all the hoses. I cleaned it with solvent, blew through it, and reinstalled it. Now that I think about it, it was not too easy to blow through the valve. The tank would have to build up a pretty good amount of pressure to release the valve. However when removing my gas cap there is never any pressure build up.

[joelbert2k]

When I got home today I removed my gas cap. There was a lot of pressure built up. I need to look at how all these vent lins should be run and figure this thing out.
Joel