petrol return pipe ?

Willy · Post by **Willy** » Fri Feb 24, 2012 11:15 pm

Not a great photo, but here goes:

Pipes to/from tank to the right of the cambelt cover, "in" pipe goes to primer pump (gold on fireboard), fuel line to mechanical pump (we all know where that is), through in-line filter (behind air duct) and enters the round thing (???) below the carburettor as the top pipe. The bottom pipe from that clearly travels to the carburettor. However, it also has a third hose (the middle one) that as you can see is the elusive return pipe and can be traced back to its exit hole under the primer pump.

Now, time to tell me where I'm going wrong again

BX Meteor · Post by **BX Meteor** » Fri Feb 24, 2012 11:30 pm

I think it was where you said "my 1.6 has some internal leak somewhere causing all the fuel to drain out of the system back into the tank overnight, and the float bowl evaporates very quickly too."

I would have asked for a pic of the car but I thought the youtube thing was yours. But wow Bob's car looks cleaner than I remember from the ebay pics

Amyway ...... how could fuel get out of your float chamber, past the needle valve, back down into "the round thing" ?

And, how does it get uphill from "the round thing" back to the tank (and how do you know "the round thing" is empty) ?

"there's a hole in my bucket, dear Liza dear Liza"

Willy · Post by **Willy** » Fri Feb 24, 2012 11:52 pm

BX Meteor wrote:I would have asked for a pic of the car but I thought the youtube thing was yours. But wow Bob's car looks cleaner than I remember from the ebay pics

It didn't look like this when a coolant hose was flying around spraying orange liquid over everything! Also, it's hard to see, but the tiiiiny amount of rust encroaching around the top of the strut - worry or not worry?

And anyway, you ask me questions to which I don't know the answer, whoever assigned the "BXpert" tag to my handle is as misguided as I am!

Re the float chamber though I thought we'd already established that it is probably evaporating out, the rest of the system is a mystery

Mickey taker · Post by **Mickey taker** » Sat Feb 25, 2012 12:07 am

don't think I have the three pipe thingy and if I have its been bypassed.
I only get petrol smell on start up , I thought it may be because the electric pump starts as soon as you turn the ignition on to starter position and will obviously be pumping at the same rate as it would if the cars running unlike the manual pump which increases and decreases in speed in relation to how fast the car is running.

Way2go · Post by **Way2go** » Sat Feb 25, 2012 1:39 am

SU pumps sense the back pressure so will only electrically pump when the float valve is open in the carburetter. Hence your "round thingy" has probably been binned by the person doing the replumbing!

Way2go · Post by **Way2go** » Sat Feb 25, 2012 1:47 am

Also you should be aware that your mechanical pump if not FUBAR at the start of this exercise, probably is now if it has been run dry all this time. There also could be a fire/explosive danger if damaged seals allow petrol to flow into the oil sump via the drive shaft upon re-instatement!

BX Meteor · Post by **BX Meteor** » Sat Feb 25, 2012 3:13 am

Way2go wrote:SU pumps sense the back pressure so will only electrically pump when the float valve is open in the carburetter. Hence your "round thingy" has probably been binned by the person doing the replumbing!

Mick, he's right !! I'm trying to find out what it is, it says "SOFABEX" on it.

Way2go wrote:Also you should be aware that your mechanical pump if not FUBAR at the start of this exercise, probably is now if it has been run dry all this time. There also could be a fire/explosive danger if damaged seals allow petrol to flow into the oil sump via the drive shaft upon re-instatement!

Mick, he's right again !! Pump is also "SOFABEX" so it might be worth sourcing the pump and "round thing" as a pair.

.... until then. yo're stuck with that plumbers heaven in there

(the fire gods in the forest will have to wait)

Post by **Defender110** » Sat Feb 25, 2012 8:20 am

Way2go wrote:Also you should be aware that your mechanical pump if not FUBAR at the start of this exercise, probably is now if it has been run dry all this time.

But it hasn't been run dry has it? , it is strangely still plumpbed into the system with fuel flowing through it all the time is it not. Personally If fitting an electric pump I would have thought bypassing it would have been the way to go.

Post by **Defender110** » Sat Feb 25, 2012 8:34 am

If I remember rightly Bob fitted the electric pump to try and eradicate bad starting not because of running problems. If he primed the system it would start instantly, if he didn't you had to crank the engine for an age to get fuel up before the car would start. I'm no expert when used with petrol but when this type of mechanical pump is fitted to a diesel it relies on the 2 one-way valves fitted in the pump to stop the fuel returning to the tank when not running. If these little diaphram valves get a little bit of crud stuch on their seats they no longer seal and the fuel runs back. They often just need the valves cleaning and they are easily accessed by taking the pump apart with the ring of screwa round it's diameter. Bad running can be down to the main diaphram being split which limits fuel delivery all together.

Willy · Post by **Willy** » Sat Feb 25, 2012 10:22 am

Defender110 wrote:
Way2go wrote:Also you should be aware that your mechanical pump if not FUBAR at the start of this exercise, probably is now if it has been run dry all this time.
But it hasn't been run dry has it? , it is strangely still plumpbed into the system with fuel flowing through it all the time is it not. Personally If fitting an electric pump I would have thought bypassing it would have been the way to go.

True, but as you can see the outlet connected to the inlet so just as an infinite loop. You may have then been recycling crud through the diaphragms, or, if it was just left "dry", then maybe the diaphragms degrade faster if they are not lubricated with fuel? Even if neither of those were the case then I'd replace anyway, they're not much money, and for all we know the pump you have now may have driven 100k and be well past its sell-by-date anyway.

Re Kevan 2nd comment, I thought of fitting a one-way valve after the fuel pump to stop petrol draining back through there, but shouldn't a good working PD pump act as a natural one-way valve anyway?

BX Meteor · Post by **BX Meteor** » Sat Feb 25, 2012 1:32 pm

Willy wrote:
Defender110 wrote:
Way2go wrote:Also you should be aware that your mechanical pump if not FUBAR at the start of this exercise, probably is now if it has been run dry all this time.
But it hasn't been run dry has it? , it is strangely still plumpbed into the system with fuel flowing through it all the time is it not. Personally If fitting an electric pump I would have thought bypassing it would have been the way to go.
True, but as you can see the outlet connected to the inlet so just as an infinite loop. You may have then been recycling crud through the diaphragms, or, if it was just left "dry", then maybe the diaphragms degrade faster if they are not lubricated with fuel? Even if neither of those were the case then I'd replace anyway, they're not much money, and for all we know the pump you have now may have driven 100k and be well past its sell-by-date anyway.

Re Kevan 2nd comment, I thought of fitting a one-way valve after the fuel pump to stop petrol draining back through there, but shouldn't a good working PD pump act as a natural one-way valve anyway?

Willy, you've slightly misunderstod what Kevan said in his second point, which is a good point, I'll explain it.

He means that the fuel may drain back in the pipe from tank to pump, NOT from the carb. This means that if a bit of fuel has also evaporated from the float chamber, then the fuel level on the float chamber does not have enough "height" to provide enough "pressure" to the jest (I keep saying, the correct level in the float chamber provides a tiny pressure to the jets).

So. a slightly reduced level in the float chamber (due to evaporation), a drained pipe between tank and pump .... and there's one's starting propblem

i.e. the starter motor has to crank the mechanical pump until it has sucked fuel into the empty pipe between tank and pump, and then it can start to provide pressure so that the level in the float chamber gets a few mil higher, so now the fuel vapour will be drawn off the jets by the venturi.

As I said before, fitting an electric pump will tackle the symptom, without figuring out what the disease was in the first place.

Way2go · Post by **Way2go** » Sat Feb 25, 2012 1:38 pm

Defender110 wrote:
Way2go wrote:Also you should be aware that your mechanical pump if not FUBAR at the start of this exercise, probably is now if it has been run dry all this time.
But it hasn't been run dry has it? , it is strangely still plumpbed into the system with fuel flowing through it all the time is it not. Personally If fitting an electric pump I would have thought bypassing it would have been the way to go.

The mechanical pump will be as dry as it is possible to be even if it was originally left with petrol in it as it is not part of the system but has been connected in short circuit mode.

Perhaps it was filled with light oil before the short circuit was applied and therefore could be in better shape but who knows? It has really just been left in place to seal a hole in the block, not for re-use later. I would not risk re-using it.

BX Meteor · Post by **BX Meteor** » Sat Feb 25, 2012 1:40 pm

Whose car are we talking about, Willy's, or Mick's ??

EDIT:
on Willy's (which I think Kevan is talking about) the mechanical pump is still in the circuit
see pic of Willy's system here

on Mick's (which Mick wanted advice about) the mechanical pump has been connected in short circuit mode
see pics of Mick's system here (re-edited cos url was wrong)

So if posting, please make sure you say "Willy's car" or "Mick's car"

Way2go · Post by **Way2go** » Sat Feb 25, 2012 2:04 pm

This is Mick's thread so I am talking about Mick's car as he is the one proposing re-instating his system and requesting help.

The other system is not relevant to the problem and is off-topic as we are not comparing eggs with eggs!

BX Meteor · Post by **BX Meteor** » Sat Feb 25, 2012 2:09 pm

Willy, you're a naughty boy

Kevan, forget Willy's car

Mick, have you got any help from all this