My Paso 906 has the Weber carb and the restictor jet in the return fuel line to the tank. I was told that the fuel pump runs constantly but mine beats at a rate faster than I can count maybe at least 5 times a second - if not more when I just switch the ignition on without the engine running. Obviously I can not here it when it is running. Is this normal ?

What you are describing is a classic no load on a motor condition.

Applied electrical engineering when there is little or no load on a motor it will spin at its highest design i.e. (1,200 / 1,800 /3,600) RPM. Example if you hold your hand on the inlet hose of your shop vacuum the motors quickly moves to high speed because it’s not sucking any air, it’s not doing any work.

It sounds as if the restrictor you mentioned may have reduced the pumping load on the motor by a high measure. The standard Paso pump runs between 3 to 5 PSI. Try running without the restrictor and observe the difference.

I have found my Paso 750 runs better at the lower 3 PSI level. I use a Weber redline fuel pressure regulator #31800.063 in the supply line between the pump and the carburetor to adjust the fuel pressure.

Sounds fast . Mine has a rotory pump that spins rather than pulses and I use a long piece of 1/8 inch tube for the return line instead of the restrictor jet and I set the length by adding more length until the pump started to sound like it was working a wee bit. I have no idea what pressure arrives at the pump but its more than none and its enough so that it can keep fuel up to the carb during my land speed attempt ( that was a miserable disappointment ....... flat out at 210kph.... my tractor goes faster than that !). I was working on the theory that I needed enough pressure to keep fuel up to the carb with a bit to spare ( hopefully about 3-4 psi ) but not the full pressure the pump was capable of , which is about 7-8 psi

So does it sound like a problem with the restrictor letting too much fuel back to the tank or is it a fault with the pump, although this seems to be doing what it is meant to do. I will try blocking the return to the tank to see that the pump stops beating. Any other suggestions ?

I guess blocking off the return line will tell you if the pump is ok , if it still pumps there may be an internal leak , like maybe a hole in the diaphragm. I think that if I ever ( bound to ) have to replace the pump I'll go for the manifold vacuum/pulse operated pump off the monster ( or similar ) heaps of bikes ( and other engines , outboard motors ) ) use them so I spose the cheapest suitable one will get the nod .
Regards
Hamish

I disconnected the return line to the fuel tank and switched the ignition on. The pump filled a small cup with petrol in about 30 seconds. If I then blocked this pipe the sound and therefore the rate of pumping decreased but did not stop. Again is this normal or should it stop.

I would think it should stop , but I am not 100% sure

My feeling is that it should stop as well. It may be the relay which is not functioning. Either way I think it is replacement time.
The vacuum operated pumps from the Monster etc, do they function OK with the Weber carb. Do they stop the flow of fuel or would I have to rely on the Weber to do that.

OK if I went for a vacuum operated fuel pump for use in my set up with Weber carb and no further modifications then do I take the vacuum after the "T" piece on the way to the Digiplex. ?

Good question , I think that the reason for the T piece for the digiplex is that the pulses from 2 cylinders are going to be smoother than just one , providing a more even vacuum signal , which is exactly what you don't want for a vacuum operated pump so I would preferably fit another vacuum take off to one inlet , drill and tap a 5 or 6mm hole and use a cap screw with a bit of shank on it , trim it so there is 5mm of thread and 10mm of shank by cutting both ends off and then run a small drill thru it from end to end
. You could just fit another T between the existing one and one side of the carb but I don't think you'd get as strong a pulsing signal and that is what drives the pump . Ive had a butchers at my monster service manual and the only thing it says about the vacuum pump is that its held on by 2 bolts and you cant fix , test or get parts for it. I spose the closer to the manifold you can get it the better but having said that the one on my quad has 2 feet of vacuum hose between it and the manifold and it works great.
Hamish

I have a dissenting opinion, yea big surprise...unfortunately I am currently under the influence so will speak up at a later date

Now I am interested in this discussion as this is not an area that I have any real expertise in. So much so that whilst waiting for the contra-view from Higgy I have had too much to drink.

Yeah well my liver hasn't yet fully recovered from being smeared around my spine so Im on the O J ( this oughta be easy ) , Oh how I look forward to attempting a constructive discussion with inebriated experts ..... usually ends up in the car park . Higgy I look forward to your sobering reflections , Giscard , don't make another rash decision whilst plastered ( I take it your already married ) ...... and I think I will have a wee Benedictine... or two ...... medicinal reasons