6V fuel pump

[brian]

I am beginning to think that my Aprilia's failure to run for any time at higher revs (see Aprilia tank removal!) is down to the new fuel pump fitted on its engine rebuild.
To test this hypothesis (at least the 3rd so far) I have searched online and there are posts from USA about fitting 12V pumps on 6V cars and its working perfectly. This would save me buying a different pump as I have a few Flavia ones lying about. If it does work, all well and good and if not I need a Hypothesis 4.
I cannot see a way of increasing the flow on the Airfix E8011 that was fitted.
Has anybody any ideas on this before I do the deed?

[Mikenoangelo]

Have you tried it since sorting out the fuel supply pipe? An air leak between tank and pump seems a likely cause.
Mike

[simonandjuliet]

Have you thought about running without an electric pump - the mechanical pumps are v good and I recently had some new ones made that are now available at a reasonable price ( in France). Just make sûre the gaskets are not too thick and the rod not worn. Others have fitted 2 cv pumps but you need to change the pipes if it’s not an original set up

[brian]

I did have a small leak at the flexible hose near back of car but problem persisted after sorting.
The car had an electric pump when I got it and so I assumed it was a reasonable thing to do and the old one worked well until the engine rebuild when for reasons I did not know it needed replacing. On the car at ther moment is an Airfix E8011 said to deliver at 5-8PSI.

[JohnMillham]

On the car at the moment is an Airfix E8011 said to deliver at 5-8PSI. That sounds like too much pressure. 2 or 3 p.s.i. is usually plenty. I use a pressure reducing valve on my Lambda, which seems to work OK.

[Raahauge]

Have you tried disconnecting the feed to the carb and pumping the petrol into a (measured) container?

[brian]

Please excuse my ignorance but:
1. How does a higher pressure than that needed cause a drop in available fuel at the carburreter?
2. What would I be looking for if I disconnect the outlet and measure the volume? I did this and "lots" came out - a little fountain not a dribble.
Brian

[GG]

Have you tried putting a pressure gauge on the fuel line and seeing what is actually delivered? Not too sure about Aprilias, but on Aurelias, we found the pressure varied immensely by the rod and the gasket thickness (as noted above, thank you!). Just the gasket thickness itself, was enough. And the elec pump on the Aurelia ran through the mech'l pump - so more pressure didn't really matter at all (actually, would hurt the mech'l pump with too much on the diaphragm).

[DavidLaver]

Not sure its the answer here (pretty sure its not the answer here...) but an idea:

https://www.ebay.co.uk/itm/Sealey-1-Litre-Portable-Fuel-Tank-Ideal-For-Test-Beds-Or-Temporary-Start-Up/141957834894?epid=1005385530&hash=item210d58a88e:g:V94AAOSwBc5cwF9M&frcectupt=true

The assistant sits in the passenger seat holding it at different heights to vary delivery head?!!!?

Hang it off the rear view mirror???!!!!!!???!!!

Is there a rolling road locally to run tests in "laboratory conditions"?

[davidwheeler]

I have fitted a Flexolite 6v pump and a Filter King filter/pressure valve from here https://www.flexolite.co.uk/cat.asp which works perfectly and seems to be the correct pressure.  It is in the boot close to the tank thus obviating any trouble with vacuum leaks.

[brian]

It is beginning to look like an issue in the Zenith 36V12 carb as if I run at moderate revs it empties the float chamber. Pump generates a flow of about 1L/min when no carb attached to line. If bowl off I can get a fountain of fuel over the right side of the engine bay and stop it by pressing the cut-off in the carb top.
Brian

[brian]

Hallelujah!!
Finally sorted and as suspected was something trivial. After the last check I was putting the float chamber back and was struggling to keep the gasket in place and I just wondered if this was the problem and so put a couple of dabs of blue Hylomar to keep it in place whilst I slid the chamber back. I then started up and ran for 10 mins at half throttle with no hint of misfire. Just driven 25miles on A38 at 45-50MPH with not a single misfire.
Answer therefore was that the carburreter rebuild was fine except for the gasket was crumpled over a jet or cut off valve and if driven below 40MPH enough petrol got through but faster the flow into the chamber was reduced and spluttering etc.
I was discussing with my friend who has a Stag and he eventually found a similar symptom was due to a hair ball in the fuel line in a wide rubber bit between the copper pipes and at low speed enough fuel got through but at higher flow the hair compressed and reduced the flow.
Thanks for all the advice which did help to rule things out.
Brian

[DavidLaver]

Great news...