You could be technically right on the SU pump as I havnt had one apart for a
LONG time, But even if it stalls out or slows down at a known pressure it is
still acting like a pressure shut off (otherwise it would be capable of
infinite pressure!). I remember it either stoping or becoming very quiet
upon full pressure. And drain back will definately occur with some fuel
pumps, and I did ask the original lister what pump he was using as it does
make a difference.
The drain back can work both directions(towards the carbs), depending on the
state of his evaporative loss system too.
Speaking of Fuel expansion: In my early days I remember I had just filled
up my 70 MGB to the brim with fuel. After it was parked for a while in the
hot sun I noticed a ton of fuel spilling out the filler around the cap...I
was scared!! I never filled it that full again...live and learn.
-----Original Message-----
From: Neil Sherry [mailto:neil@sherry02.freeserve.co.uk]
Sent: Thursday, July 15, 1999 6:06 AM
To: Drew Stieber; waltcpa@sierra.net; mgs@autox.team.net
Subject: Re: Fuel stuff
I'm afraid I must disagree slightly. As far as I am aware the SU pump does
not have a pressure shut off as such - it just stalls out (or slows down).
Secondly there should be no drain back to the tank as the pump has two non
return valves in it. Drain back will only happen if these leak (Ideal
situation. Reality is probably some leakage). The lack of fuel in the line
is more likely contraction of fuel during cooling after engine shut off and
heat soak caused expansion.
Neil
-----Original Message-----
From: Drew Stieber <dstieber@PACCAR.com>
To: 'waltcpa@sierra.net' <waltcpa@sierra.net>; 'mgs@autox.team.net'
<mgs@autox.team.net>
Date: Wednesday, July 14, 1999 1:40 PM
Subject: Fuel stuff
>The circular can behind the Rt side tire well in the trunk is a vapor
>seperator canister. It is part of the evaporative loss system. It is
>possible for fuel to be in the hose from the tank to the vapor canister
>itself. If the hose breaks in this area it could leak some fuel into your
>trunk.
>
>If you over fill your tank and do some hard acelerating and your filler
>gasket is bad the gas can also slosh out into your trunk. MG tanks have
>short filler necks and it is possible to overfill a tank. Modern vehicles
>have filler necks which serve as a buffer for sloshing and are usually a
>foot long or more. AN MG filler is more like 6 inches or less. Also if
>your car has some rust on it you may have holes in the top of the tank.
>
>What type of fuel pump do you have? An SU Pump has a pressure cut off and
>it will stop when it gets to a preset PSI. An after market pump may or may
>not (it is OK for them to just keep pumping as they have a release valve
>inside). It is not unusual to not see fuel at the carb hose unless it is
>under pressure (the system is on) as it is the highest point of the system
>and gravity pulls the fuel back to the tank. Ever notice that the pump
>clicks a bunch when you first turn the ignition key and than stops? It is
>priming the system. Although that epends on your fuel pump too.
>
>
>Good luck.
>
>Drew
>
>
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