running issues

[amam]

my running issues on my 126 kit car seems to be down to one problem

ive changed the fuel pump, changed the sender unit, checked the fuel tank, made sure the breather is clear and made sure the pipes are the correct way round on the sender unit

but still when i rev the engine you can see bubbles travel up the pipe from the fuel tank into the fuel pump and then air in the clear fuel filter, once this goes to the carb is causes it to cough and when driving it doesnt pull well

ive even run the engine off a bottle of fuel into the fuel pump and its fine

what im confused about is if the sender unit is submerged in fuel (3 quarters of a tank full) then how can air be traveling in the fuel line and only when you rev it?

really baffling me

[Xylaquin]

What about the fuel lines and their clamps?

Essentially when you rev the engine the pump is sucking harder. Perhaps the air leak is only occurring when there is enough suction to strain minute leaks in the line itself...

[Rusty's Uncle]

Do you know the condition of the fuel tank. If you have any fine rust particles in there they block the inlet pick up filter and lead to fuel starvation

[drcdb15]

Here's one thing you might try: give the fuel tank a good thump to loosen any rust residues inside - obviously don't beat the carp out of it or dent it, but a few minutes of steady knocking all over with a rubber mallet... Then depending on what you have to hand, and the location of the tank, try to gather all the rust particles with a strong magnet. On the CC Zero the tank filler tube is a simple straight vertical tube - you can literally look down into it and see the fuel (preferably not while smoking...) so lowering in a magnet on a string is easy. You could do the same on a standard 500 tank. On the Bis as I recall the filler tube is a long S shape so not so easy. I don't know how it is on the MCA. If you can 'swirl' the magnet around a bit it will help too.

If you don't have a magnet you might find something suitable in an old radio or motor. Try first scraping a load of rust dust onto a sheet of paper, then drag the magnet across underneath the paper and see if it pulls all the dust together. If it does, then that will be strong enough to collect rust within the fuel tank. Or you can buy one on eBay for a few pounds http://www.ebay.co.uk/itm/Traditional-Horseshoe-Magnet-Education-Science-25-x-22-x-8mm-x1-/321962382410?hash=item4af674144a%3Ag%3A46QAAOSwFnFV9ZpV

If on your very first 'dip' into the tank the magnet comes out thickly covered in brown goo, then I think you can be sure you've found the problem. You'll need to clean the magnet and keep on fishing until it comes out clean.

Sadly just attaching a magnet to the outside of a steel fuel tank won't work as the steel will channel the magnetic field through itself, and there will be no magnetic field on the inside of the tank - so any rust will continue to float around in the fuel.

MAKE SURE the magnet is VERY FIRMLY attached to the string, because if it comes off in the tank you'll never get it out. It will stick to the steel.... being magnetic ... 

[michaelodonnell500]

Before dropping the tank you could rule out the fuel pipe first.
If the car ran fine from a bottle of petrol, move the bottle to the petrol tank, disconnect the fuel line from the tank and drop it in the bottle.
If the engine still runs well it is time to drop the tank.

[stephenc]

I read somewhere that dropping a couple of handfuls of sharp pea gravel into an empty fuel tank and giving it a really good shake will get rid of any flakey rust.

[ChrisRLewis]

It maybe worth checking the sender unit, there's a small filter on the end of the pick up pipe, possibly blocked?

[drcdb15]

I read somewhere that dropping a couple of handfuls of sharp pea gravel into an empty fuel tank and giving it a really good shake will get rid of any flakey rust.

Yes, this is a commonly used technique (or was when I was a lad...) but it requires the tank to be removed. Even then, a fuel tank can be a pretty unwieldy thing to literally give a good shaking to. The technique was commonly used for motorcycle tanks, which were easy to remove and to handle. A little fuel in the tank helps too, to swirl the flakes away from the tank wall.