Carb Fuel Pump - aaaarrrrrrggghhh

[Mongoose-99]

I have just fitted a new original Bosch fuel pump (Part No. 580960009) to my Weber carbed 1971 911T.

This was supposed to cure my fuelling problems after the expiry of the old pump, and a further 6 week delay caused when the parts supplier inadvertantly shipped me a high-pressure MFI pump - an error which only came to light when I plumbed it in and powered up the pump...

Now the d*mn thing doesn't seem to be flowing enough fuel to the carbs. I can start the car from cold, and then run it on idle in the garage. On the last two occasions I then tried to take the car around the block, it died with what seems like fuel starvation within about 1 mile - failing to restart, and needing towed home on each occasion behind my good lady wife's jeep.

After suffering the normal 20 minute monologue questioning my sanity for buying and trying to run such a heap of fine German engineering:

I checked the pressure in the carb supply line - which seems OK at 3.5 psi, but the flow rate (measured into an empty container) is somewhere around 1 pint of fuel / 4 minutes i.e. 1 gallon per hour - vs. a specified rate of around 20 gallons per hour .

In terms of things I have changed from the previous installation, I have added in-line filters to the supply line from the tank, and the supply line to the carb. To do this I have had to use fuel line and connectros which in some sections drops to inner diameter 6 mm (1/4 inch) . Also the positioning of the filters means that they sit at high spots in the system - and as a consequence seem to be between 1/2 and 2/3 full of air when running.

Is there anything you guys recommend I should do or check prior to tearing the pump out and sending it back (again) ?

Any help gratefully appreciated.

[304065]

You have answered your own question! If you aren't getting sufficient flow, there must be a restriction in the line. Take out those filters and see if it works better. If they are full of air, that's really an indication that something is plugged, filter installed backward, obstruction in the line somewhere.

[Mongoose-99]

John - your comments on the restrictions are valid.

The air in the filters puzzles me though: if the filters are located at the top of what is an inverted 'U' shape in a pipe run - at a level higher than that of the fuel tank - any air in the lines will flow to that point.

Qn: Will it adversely impact the flow rates, and if so - how do you bleed it off ?

[silverc4s]

Is your pump mounted up front, or at the engine compartment? I solved my flow problem to Webers (previous 911) by removing the pump in the rear, and mounting it in the steering compartment underneath, up front. They push better than they pull fuel, I think....;-)

PS. You should still get that thin line out of there. Put your filters right by each carb,then you can see the flow. PMO's new weber fuel bars have an integrated filter, soild though, not see through.. Good Luck!

[john walker's workshop]

it's a old car, and the tank may be rusted inside. particles of rust can block the filter screen in the tank. remove the fuel sender and look in with a flashlight. the screen can be seen thru the hole also. i can't believe a new pump would not flow more than that.