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Discussion Starter #1
Hi Folks, I need to troubleshoot a potentially fuel related problem,

The car is a Spider 2000, 1976, euro spec, dual Webbers and mech fuel pump (which is brand new, purchased from Classic Alfa). The fuel system has an inline fuel filer and a Malpassi fuel pressure regulator (with its own filter). Fuel lines are new. Carburetors have been revised recently with a set of new gaskets. The carburetor mounts have also been replaced with used Pirelli ones, in good condition, 1,500 miles ago.
Battery is ok
Starter is ok (brand new)
Spark it ok
Local temperature : 104F

After traveling 1,300 miles in 4 days without a hitch, here’s what happened.

I arrived at my folks’ town (the car tank was half full) 2 weeks ago. I topped it off and parked it in our garage, where it sat for 2 weeks straight (we were at the farm during this time).

When I came back and I tried to turn it on, It took several attempts to start the car (at least 15 minutes trying). When it finally started, everything was fine. It idled normal.

I waited about 10 min to warm it up properly and took it for a spin. It run fine. When coming back home I noticed it was dying at the red lights when I stoped.

I got at my parents home and parked the car. 30 minutes later we were about to leave for dinner, I started the car, it run for a couple of minutes and died...I tried again, and the time the engine run before dying got shorter and shorter...until I could not get it to run. It starts and dies right after.

I called a local mechanic to help and the next day we checked. The inline fuel filter was dry. We thought it could be a vacuum leak, although the roses did not show any visible sign of tear or leaks. We pulled gas back though the system and it fired and run fine.

After about 12 miles the same problem. Tried to start the car after parked for a few minutes, it fires and died light after.


This time we towed it to the mechanic and after checking the filter was dry again...

We checked the roses more carefully and did not find any leak...

Finally we decided to disconnect the Malpassi fuel pressure regulator (brand new) and the problem stopped, so far.

I’ve since driven about 30 miles, including some road, and had one event of the car dying in a red light after coming back. I thought I was going to get stuck again but this time after I fired it it kept going. This was last evening and since then it hasn’t had the problem again (I drove the car to the office this morning).

Im still not sure what the problem really was and I’m still not confident to take the long road back

Any clues would be enormously appreciated !

TIA

Gui
 

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Check the gas tank vent.
 
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But Mad North-Northwest
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You don't want a filter between the tank and the fuel pump. The carb'd cars did not have one, and it can cause flow problems with the pump.

If you've got the regulator/filter after the pump that's all you need. Jim's advice to make sure the tank is properly vented is also a good one.
 

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When it "dies" does it respond to the throttle, meaning that it wouldn't die if the idle screw was set a bit higher? Is there any sign of debris in the inline or malpassi filter. I agree that the in line filter isn't required. I assume that the feed from the fuel tank goes to the pump, the outlet from the pump goes to to filter regulator, the outlet from the filter regulator goes to the Webers. When you remove the cap on the fuel tank, does it "hiss" - it shouldn't if it is vented properly.
 

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I would begin at the source. Remove the float assembly and look into the tank. If it is not absolutely clean and tidy, remove it and clean it and reseal it. Inspection of all the delivery and vent lines would be next. GLWYP.
 
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Discussion Starter #6
Thanks for the valuable feedback folks.

I indeed wondered if the inline filter + fuel regulator and its filter would add too much head loss in the system and push the pump out of its designed operating point (head x flow). I work with hydraulics and this crossed my mind. The mechanic said not to worry.

It is a fact however that the car run about 2,000 miles with this setup with no problems from day one, so it could either be a new issue (vacuum leak ou bad gas) or that a cumulative stress on the pump leading to some damage.

Malcolm, when the problem happened, pressing the throttle caused the engine to die out. I done recall hearing the hissing sound from the tank. The setup was: tank -> inline filter -> pump -> Fuel regulator -> carbs

I still have to remove the Fuel regulator to check for debris or damage. I did check the carbs fuel inlet, and those little plastic screens, and they are clean and pretty. The problem hasn't came back so far.

Gui
 

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Discussion Starter #7
Just an update

After some further testing, we nailed it down to a likely faulty inlet valve at the pump.
When the diaphragm moves down to create suction, this one-way valve opens up and gas is sucked into the pump chamber. When the diaphragm moves down and compresses the chamber, the inlet valve is pushed down and closes, while the exit valve opens up to let the gas exit.

I understand this it most likely common knowledge, I'm just typing it here so anyone can correct me if this pump is different...

According to the mechanic, the inlet valve is letting fuel pass back through it during pump operation...maybe it is stuck open ? this explains why the car is chocking when I apply the gas

As a temporary fix, I bought this electric solenoid pump to be hooked up in the system right before the mech pump. This is a cheap pump (20 dollars here in Brazil). It is a low pressure pump to work in carbureted cars.Has anyone seen anything like it ?

Gui
 

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Electric pumps like that work better pushing fuel, than pulling it. I would install it under the car, closer to the tank.
 
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