Carb Issue ?
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Hi,
I think if the return ins unrestricted the pressure should come back down.
Cheers,
Gavin :)

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Right then,
First of all i got another pipe from the return of the regulator, going into a petrol can.
Tested it, and all was fine. i then took the pipe off the return on the petrol tank, then on the regulator. gave it a good blow a few times.
which seemed fine.
I then attached the return back on the regulator, and the return pipe for the petrol tank into a petrol can. tested it, and back to where i started, to much pressure. i checked the return on the tank side, and the fuel seemed tobe flowing fine in the can ?
So what do you think ? im lost.
I can't see it being the breather, as i checked it with the return not on the tank. confused

Cheers lads

Shit Happen's

Schrödinger's cat - so which one am I ???

Hi,
Rod's right on the money
Cheers,
Gavin :)

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I agree Rod, if you've got 2 gauges you could put one at each end and measure the pressure drop?

What pump are you running, if its got a high flow rate the regulator/return line might not be able to cope with the flow.


EDIT: thinking about it you could test the pressure drop by placing the gauge at the fpr end of the hose (take reading) then place the gauge on the tank end of the hose and compare readings for pressure drop?

Edited by matty on 1st Sep, 2008.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Theoretically the pressure at the far (tank) end of the long return line will be zero anyway (maybe a little bit above if it goes in below fuel level) so.....

Markie, can you put a Tee piece in the return line just as it comes off the regulator, before it goes back to the tank and run the pump, with the pressure gauge connected there.

This will show if there is a pressure restriction in the return line.

Schrödinger's cat - so which one am I ???

Shit Happen's

Shit Happen's

The eBay link in the thread from when you bought is dead now (too long ago for the listing to still show) but was it one of these by any chance

http://cgi.ebay.co.uk/NEW-Electric-Fuel-pe...id=p3286.c0.m14

Schrödinger's cat - so which one am I ???

Shit Happen's

Yes, gauge fooked, that is showing about minus 2.5psi

If you were getting 6psi (plus the offset on the gauge, ie 8.5psi) and you were tee'd into the return line at the regulator (the one back to the tank) then either,

a - there is a serious restriction in that line back to the tank (or line too small/pump too big), or

b - are you absolutely sure you have the regulator connections correct.

EDIT - basically the return line should be next to zero pressure as it's just returning unwanted fuel to an un-pressurised tank. It will have a very small pressure at the regulator because laws of physics say there must be some pressure drop down the line but it MUST be at a significantly lower pressure than what you're trying to set the outlet of the regulator to, ie significantly less than 3-4psi. I would expect about 0.5psi on a large return line, maybe 1psi on a small one.

Edited by Rod S on 1st Sep, 2008.

Schrödinger's cat - so which one am I ???

On 1st Sep, 2008 Rod S said:
Yes, gauge fooked, that is showing about minus 2.5psi

If you were getting 6psi (plus the offset on the gauge, ie 8.5psi) and you were tee'd into the return line at the regulator (the one back to the tank) then either,

a - there is a serious restriction in that line back to the tank (or line too small/pump too big), or

Answer,
Well like i said, it's had this setup for 8 years now. and the fuel pump has been on since jan 08 with no problems.
Im lost now :( unless i can get my compressor in the week and blow down the line with it, just incase there is a little bit of crap down there ?

b - are you absolutely sure you have the regulator connections correct.

Yes mate.
This is how i have it.


EDIT - basically the return line should be next to zero pressure as it's just returning unwanted fuel to an un-pressurised tank. It will have a very small pressure at the regulator because laws of physics say there must be some pressure drop down the line but it MUST be at a significantly lower pressure than what you're trying to set the outlet of the regulator to, ie significantly less than 3-4psi. I would expect about 0.5psi on a large return line, maybe 1psi on a small one.

Edited by Markie_D on 1st Sep, 2008.

Shit Happen's

If i end up changing the steal pipe. should i get steal, or copper. and the same 6mm or get 8mm copper or steal pipe.

Cheers.

Shit Happen's

OK, agree with connections so if you are getting 6-8psi on the return line next to the regulator, there is a serious restriction back to the tank.

This is confirmed by your earlier test of return straight into petrol can and the regulator seemed to work.

My personal thoughts.... others may disagree.

The pump you have used isn't wrong, but it's not ideal.

I know others have used them and I bought one too for my project, but I bought it because if you read the eBay listings carefully you will find it is a generic 3bar pump for a whole load of fuel injected cars with external (not in the tank) pumps. I bought it because I'm doing fuel injection.

For the carb, which doesn't need anywhere near as much pressure as fuel injection, is is probably too good.... ie, it needs a bigger return path when the regulator is calling for lower pressures.

This seems to be borne out by the fact you got the regulator to work with a short return straight into a petrol can but not on your longer tank return.

I would suggest you repeat the test with the regulator return straight into a can and prove (beyond doubt) the regulator works and if it does, decide whether to use a smaller pump or a bigger return pipe - I get the impression the majority of your return is only 6mm..... don't most people on here use 8mm or bigger ???

But, as I said earlier, I'm no expert on the SU carb setup, I'm much more familiar with injection systems.

Schrödinger's cat - so which one am I ???

Hmmm im not sure really.. it's be fine for 8 years till now.
Should i try another fuel pump ?
What would you recomend ?
Also, could the pump be playing up ?

Cheers

Edited by Markie_D on 1st Sep, 2008.

Shit Happen's

Hi,
If you've gone this far with a 6mm return you've done well, everyone on here uses 8mm.
The Micro-bore copper pipe from B&Q seems a favourite :)
Cheers,
Gavin :)

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Shit Happen's

Remember an easy way to test if you return is restricting things is to run a long length of flexi pipe to the back of the car and into the filler neck!

Not recommended for long term use, but a quick way of either confirming or eliminating that the return pipe is restricting things.

Shit Happen's

I seem to remember suggesting that a few posts back. Lol.

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On 1st Sep, 2008 Turbo Phil said:
I seem to remember suggesting that a few posts back. Lol.

Shit Happen's

shouldnt be that hard to bend by hand but it always looks sooooo much nicer and way more profesional to use a bender.

i know a few professional benders.....

Edited by Markie_D on 9th Sep, 2008.

Shit Happen's

inside mate, your good to go