nick205
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 posted on 20/11/06 at 12:10 PM |
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fuel flow vs fuel pressure regulator?
I know some of this has been covered before, but I need more info...
My Pinto with standard mechanical fuel pump, Weber 32/36 DGV carb set-up has no fuel return. It starts and runs OK, but then floods the carb and
dies.
Some people say this se-tp should work OK, others say fit a fuel return.
Obviously the idea of having to fit a fuel return system to a 99% finished car is not one I want to think about.
The question is if I fit an adjustable fuel pressure regulator between the pump and the carb will this cure the problem?
I'm not sure I fully understand the difference between pressure and flow. Would limiting the fuel pressure to the carb prevent the needle valve
being overcome and the carb flooding?
HELP!!!!
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DarrenW
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| posted on 20/11/06 at 12:14 PM |
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My pinto with 38dgas and mech pump suffers no such problems. However with red top it was awful / dangerous. Regulator was no use with the red top,
however im sure it will be worth a try on your set up as pressure is far lower to begin with.
I also found i need to replace the accelerator pump diaphragm in the carb as this was also causing leaking etc.
Is your carb in tip top conditions ref seals etc.
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nick205
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| posted on 20/11/06 at 12:23 PM |
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Hi Darren,
I rebuilt the carb with all new gaskets, diaphagm, needle valve and power valve assembly. The floats move freely and nothing appears to be
clogged.
What type of reulator did you try?
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DarrenW
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| posted on 20/11/06 at 12:31 PM |
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I cant remember the make Nick. Bought from Mac#1 - Powertec or something like that. It cost approx £25, its an inline one with big knob on the top.
What i found was that the pulsing nature of the redtop was enough to force fuel past the regulator and still overcome the carb float (or at least that
was the conclusion at the time). Redtops are rated at around 7 -8 psi ish though so way too powerful.
Iam very surprised the mech pump is overly powerful. Do you have a reg to try? I was always led to believe carb set ups dont need return lines (or at
least not old school set ups on our engines). I dont know enough about carb rebuilding to comment if their are things to watch out for.
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nick205
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| posted on 20/11/06 at 12:38 PM |
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During my build I researched it, but likewise got the impression the it would be OK without a fuel return. I have my eye on a similar type of
regulator on ebay at the minute which might give me a locost way of testing my theory.
I really can't contemplate having to mess about fitting a fuel return 
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westf27
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| posted on 20/11/06 at 12:46 PM |
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fuel regulator
I too had the same problem of flooding on my dcoes with a blue top pump.However i fitted a pinto mechanical pump and had similar problems,so did a
pressure check and found it producing 7 psi.Fitted a filter king pressure reg and adjusted to 3-4 psi and now i can get starvation at 100mph.Seems
like you reduce the pressure and flow rate ,not ideal ! So sympathetic to your problem but no solid solution to offer.Read about return lines and
loops around the pump maybe thats the answer? I get such a whipping at 100 mph from the harness its easier to slow down!!
555
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Surrey Dave
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| posted on 20/11/06 at 12:52 PM |
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This is why many advocate fitting a bike pump, they are supposed to give good flow ,but stop when sensing back pressure from the closing fuel
valve.
I have a facet + fuel regulator on my bike carbs but it has to be set at 1 pound so as not to flood, I'm worried about flow at the top end so I
have a bike pump to try.
Also didn't the old SU electric pumps as fitted to early minis stop when the carb was full?
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MikeRJ
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| posted on 20/11/06 at 01:04 PM |
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A mechanical pump should not require a pressure regulator, after all this is the same setup that was used in millions of production cars. The modern
viton tipped needle valves should be able to hold 7PSI comfortably.
Re. return pipe, a mechanical or electromechanical (reciprocating) pump does not need a return as the pumps are pressure sensitive and stop pumping
above a certain (low) pressure. You only need a return if the pump delivers very high pressure and flow such as an injection pump, and even then some
pumps have regulators built in so you don't require a separate return (though there are advantages in keeping fuel cool etc.).
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nick205
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| posted on 20/11/06 at 01:10 PM |
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quote:
Originally posted by MikeRJ
Re. return pipe, a mechanical or electromechanical (reciprocating) pump does not need a return as the pumps are pressure sensitive and stop pumping
above a certain (low) pressure. You only need a return if the pump delivers very high pressure and flow such as an injection pump, and even then some
pumps have regulators built in so you don't require a separate return (though there are advantages in keeping fuel cool etc.).
Mike,
How does the mechanical pump (e.g. Pinto) work?
I just assumed they were pumping all the time the engine was running and that as engine speed increased so did the flow?
Cheers
Nick
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Surrey Dave
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| posted on 20/11/06 at 01:51 PM |
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When a mechanical pump is up to pressure the activating arm is only in light contact with the cam so none or little pumping takes place until the
pressure drops
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nick205
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| posted on 20/11/06 at 02:56 PM |
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so could it be that my pump is knackered and pumping all the time?
It's the original one from the Sierra donor, so an unknown quantity in terms of performance.
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MikeRJ
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| posted on 20/11/06 at 03:12 PM |
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quote:
Originally posted by nick205
How does the mechanical pump (e.g. Pinto) work?
Basicaly an eccentric lobe on the camshaft pushes the operating arm on the fuel pump, this moves the diaphragm inside the pump and fuel is drawn into
the pump. A spring pushes the fuel up to the carb and in the process returns the operating arm to bear back onto the camshaft. The strength of this
spring (and area of the diaphragm) is what determines the fuel pressure in a mechanical pump.
If the float chamber is full (and the needle valve closed), the spring can not push the fuel out of the pump, and the operating arm does not return
back to the cam. Therefore the pumping action ceases until the fuel is expelled from the pump.
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nick205
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| posted on 20/11/06 at 03:24 PM |
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Thanks Mike, that makes more sense.
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chriscook
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| posted on 20/11/06 at 05:29 PM |
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Is your float height set correctly? After i rebuilt my Dellortos the height was wrong and fuel pissed out of the jets - re-set the height and all was
fine.
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nick205
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| posted on 20/11/06 at 05:54 PM |
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quote:
Originally posted by chriscook
Is your float height set correctly? After i rebuilt my Dellortos the height was wrong and fuel pissed out of the jets - re-set the height and all was
fine.
I think so, but I've had differing advice on the right height, so not overly sure. Any suggestions on where to get accurate or practical
information?
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