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1968 Alfa Romeo 1750 Spider Veloce
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Discussion Starter #1
Looking for advice. The car is a 1968 European 1750 Spider Veloce, all stock. The car is still carbureted and original. A few parts of the fuel system have been replaced. Mainly, the mechanical fuel pump was replaced recently with a FIPSA remake from Centerline, all fuel hoses have been replaced, and my uncle replaced the original tank with one from Centerline.

Here’s the issue I am trying to resolve. The car runs fine now that I replaced the fuel pump, but when it sits in the garage for any length of time, it won’t start. It seems to not have any fuel making it to the carbs.

HOWEVER, if I leave the car in a slight nose down attitude on the driveway, it starts normally after sitting. This mean, by my non-mechanic’s logic, that when sitting on a horizontal surface, the fuel is draining back to the tank, and nose-down, gravity keeps that from happening.

Is there supposed to be a sort of siphon valve somewhere in the system to prevent fuel from draining back to the tank?

It seems like the mechanical pump doesn’t draw strongly enough from the tank to prime the carbs to start but it OK for running the car. So if there were a valve to keep the fuel forward, it should be alright, not not? I don’t know!

One piece of possibly related information: My uncle replaced the original fuel tank with a Centerline tank that has two of what looks like vent pipes near the filler pipe. I think this tank is for SPICA cars. Could this tank be the reason for my problem?

Please help me figure this out. I know I could add an electric fuel pump to prime the carbs (like a Ferrari), but I’m hoping this is a really trivial fix. Thank you!
 

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1968 1750 Roundtail Spider Euro version
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325 Posts
Fuel in the weber bowls will slowly evaporate and makes starting difficult if the car has been sitting for a while. Many owners add a manually controlled electric fuel pump to prime the carbs which eliminates the problem... search the forum to see how members have solved the issue...
 

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I have seen photos of some porsche 356 owners install a hand squeezed primmer ball under the hood like the outboard boats use to fill the float bowls. Not sure that I would do this but is another option and a cheap fix if it would work on an alfa.
 

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1968 Alfa Romeo 1750 Spider Veloce
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Discussion Starter #4
Thanks. I mean the car can sit several hours or overnight and have this problem. Evaporation isn’t the issue. I think the fuel is draining back to the gas tank and the pump isn’t strong enough to suck it up to the front. I am wondering if the wrong gas tank could have something to do with this. I’m also wondering if there was a valve in the line to keep this from happening.
 

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Oh, I would look for a pump that has a built in one way check valve then and try this. You will need the right psi for your system.
 

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1974 Alfa Romeo spider
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130 Posts
It sounds like the check valves in your new pump are not sealing completely. Either replace the pump or check into a fuel check valve to install between the fuel tank and the fuel pump.
 

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You need to understand the way a Weber works, to understand that fuel in the float bowls cannot drain back into the tank. The Weber is not a sealed system. Atmosphere air is free to move in or out from the float bowl breathers. Next fuel arrives from ABOVE the full level in the bowl.
1668793

The needle and seat, activated from the float, fill the bowl from above. Much like a toilet float and valve. The valve is not below fuel level in the bowl, so fuel cannot be siphoned back into the tank from the float bowls.

1668794

#4 in this drawing is the fuel in the bowls, #3 is the float outline. Yellow here is fuel. No way for it to be siphoned back from the float bowls. It CAN and does evaporate, particularly todays "fuel" which is infused with soluble gasses that disappear very quickly through float bowl vents.
It is possible your floats are incorrectly set for rise and drop, so fuel level is low, running, then drops a tiny bit more at hot shut down from evaporation, then too low for easy restart. If this is the case, you have set-up issues.
Webers like about 3# fuel pressure to low pressure through your fuel pressure regulator (FRB11 or Filter King unit) might cause low bowl fuel level, or it might not.
Some things to think about.
 

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1973 Spider 2L
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235 Posts
As Gordon Raymond said fuel won't drain back to the tank from the carburetors. But as others have said it will evaporate especially if the car was hot when it was parked. Your problem might b the fuel in your bowls evaporates and your mechanical pump check valve that is supposed to keep fuel in your lines after the fuel pump lets fuel leak back emptying your fuel lines causing your car to not start. Let the car sit and pull the fuel line to the carb and see if it's full of gas.
 

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Or put an electric pump in the rear and do away with the mech one. Always gets fuel when turned on and if the car sits for many days... it will prime fuel to the carb. Also it may minimize a vapor lock as well. Just my opinion, good luck
 

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1968 Alfa Romeo 1750 Spider Veloce
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Discussion Starter #10
Thanks all. I have a Facet pump to install. Where is the optimal place to mount a Facet electric fuel pump in a Duetto? There seems to be plenty of space in the engine bay near the fuel filter. Would that work OK? Does anyone have any pictures of their Facet pump installation?
 

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1968 1750 Roundtail Spider Euro version
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Try searching the forum - this topic has been addressed and will show you the solutions
 

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Where is the optimal place to mount a Facet electric fuel pump in a Duetto
Below the level of the bottom of the tank and as close to the tank as possible. The pump should be mounted vertically with the input at the bottom. Other configurations may work OK but that is the best one.
 

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Photo...

1669009
 

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If you are actually loosing fuel out of your float bowls in just a few hours I would look at the little square plate on the bottom of each carb to see if it is leaking raw gas out. With a good flashlight and mirror you should be able to see the bottom of the carbs well enough with everything all installed. Any fuel staining would be cause for more investigation.
If there is actual fuel wetness or visible hanging drips it would be important to remember that the rear carb will be dripping on or near your starter.
 

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...Aluminum Weber bottom plate.. NOT the steel back plate.
 

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1968 1750 Roundtail Spider Euro version
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If you are actually loosing fuel out of your float bowls .... Any fuel staining would be cause for more investigation.
You made me think about something with my webers.... there is this yellowish discoloration around my jet covers .... it never occurred to me that bolstering the sealing of these covers better may retard the evaporation that is obviously occurring...
 

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Here's the facts. What you see is some modern "fuel" residue, carried out by the soluble gasses in the fuel. HARD to eliminate due to the Weber design. You may also see it around the top gasket.
Modern "fuel" was designed for air tight FI systems. Webers were designed around gasoline which no longer exists. With race fuel or AV gas, years ago, we had some discoloration too. Today it's easier to use a toothbrush and Brakeclean or WD-40 to clean it off, and most will disappear. Trying to make a DCOE or other Weber air-tight (actually soluble gas tight) is not necessarily easy or useful.
Just clean it up and forget-about-it.
 
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But Mad North-Northwest
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The float chamber is vented anyway. Your top hat seal isn't impacting evaporation.
 

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The rubber (?) top gaskets, sometimes seen, were not fuel-proof with todays fuel and wrinkled up and oozed fuel. Needed to be Viton. Don't bother trying for a gas seal.
 
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