Fuel pump

[Tim Wilson]

After a rather patchy journey back from the Lambda centenary celebrations, we have diagnosed that the main problem for our misfortunes was in fact the auto vac. Having just completed a short Welsh tour and having previously by passed the auto vac with an electronic fuel pump we are still having fuel supply problems. I suspect the pump fitted has a fault but it may simply not be powerful enough to feed the carburettor. Can anyone recommend a pump suitable for my series 7 engine? Thanks
 

[davidwheeler]

Rather, look in the technical information thread where there is information about the autovac.   They are very reliable when set up and the usual problem is a sunken float.   I have fixed mine (substituting a brass carburettor float of suitable size for the original cork) and it works just fine.
An electric fuel pump should be a low pressure one, most are high pressure and would need a pressure regulator.   After all, in the normal setup the fuel pressure is about 20cm. of petrol.     Otherwise, just blow through the fuel pipe from front to back and clear out the muck.    You may find, on removing the tank drain plug that there is a lot of grot within.   Just be sure the tank is empty or you have a big enough container!

[Tony Stephens]

And to endorse David's point about grot., I have got a vintage glass bowl Zenith filter under the bonnet before the Exhausteur (Autovac). Looking at the bowl contents, it is easy to see whether anything is coming from the tank (in my case, thankfully not). It's also entertaining and instructive to watch it while the engine ticks over, because a periodic burst of bubbles tells you that the original supply system is sucking and recovering properly.
A healthy Weymann Exhausteur is fine for everyday use, only competition cars had a dual instrument to cope with long full-throttle uphill climbs (see underbonnet pictures of Mille Miglia cars).

[Dikappa]

I have, just like David, replaced the original cork float with a copper SU float, and done the return trip from belgium to Fobello last year without issues, storming the passes in 3rd gear....Altough my car has an electric pump, that is controlled by a float switch in the autrovac tank to avoid changes to the piping, it has only been used once to prime the autovac tank on startup.

[Tim Wilson]

Thanks chaps i am off to see my mechanic to discuss your replies and to see what he thinks. He did replace the old cork float in the auto vac with a new float he made for the job but sadly this has not worked......we may have another issue however....the saga continues!

[davidwheeler]

It is quite a fiddly mechanism prone to failures here and there in the way of pins breaking, also the pressure relief valve that pops up under the cylindrical cover on the nearside needs to be free and also to seal.
Having said that, I have just had trouble with one of mine which boiled down to a failed joint in the petrol feed pipe!     The vacuum pipe must also be sound of course.