| [ Total Views: 472 | Total Replies: 10 | Thread Id: 39681 ] |
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 PurpleT3
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| posted on May 25th, 2005 at 02:08 PM |
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Measuring Fuel Pressure
Over tha last few months my carbs have repeatedly flooded, despite new needle valves and numerous cleans. Before I pay lots of money to have my
carbs checked out, the carby guy suggested making sure that the fuel pump is not putting out excess pressure. Can anybody suggest how to do this and
where I can get a fuel pressure gauge. Both the carbs and fuel pump are standard.
Ain't nothin' like the wind in your hair.
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AdrianH
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| posted on May 25th, 2005 at 06:22 PM |
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You need a fuel pressure gauge with a barbed fitting on it, a tee for the fuel line and a bit of fuel line, or find a mechanic with a pressure gauge
??
You can adjust the pressure by putting extra gaskets under the fuel pump. If the above is too much, maybe whack a couple of extra gaskets under the
pump and see if it helps.
Have the float levels been checked ?
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jakjones
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| posted on May 25th, 2005 at 06:26 PM |
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Don't use the needle valves that come in the kits
use the Brosol spring type ones
IMO:party
[Edited on 25/5/2005 by jakjones]
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aggri1
A.k.a.: Aurel Griesser
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| posted on May 25th, 2005 at 06:48 PM |
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If you have a t-piece and a length of (ideally clear) hose, pressure is really easy to measure (on a stationary vehicle). Just lift the hose up in
the air. The fuel pump will pump the fuel up the open hose only as far as it's pressure can deliver (pressure head). Basically, pressure is gravity
(9.81m/s^2 at earth's surface) times density (of fuel in kg per cubic meter) times the height. So, a 1 kPa pressure will push water of density
1000kg/m^3 a distance of 0.1m up a hose. Then it'll stop. So measure how far VERTICALLY (horizontal distance is irrelevant) the fuel gets pushed
up, and figure out your pressure. Ta-da. (Make sense?). Just be careful of where you measure stuff from.
Cheers, Aurel.
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PurpleT3
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| posted on May 25th, 2005 at 08:01 PM |
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Jak, what do the Brosol spring type ones look like and where can I get them? I have reinstalled the original ones which were in there, which look
different form the ones that came with the kit.
As I wasn't having this problem before installing the kits, I tend to think it's not the fuel pump. But I think it's worth checking.
Thanks Aurel, I don't know why I didn't think of that, it's just your basic manometer. You wouldn't really even need a T, just connect a length
of clear tobe to the pump outlet, crank the motor over on the starter and see how high it rises. Now, what is the density of petrol?
Ain't nothin' like the wind in your hair.
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68AutoBug
A.k.a.: Lee Noonan
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| posted on May 25th, 2005 at 09:26 PM |
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I'm waiting for a fuel pressure meter from Seagull, Neil in WA.. I'd like to know the pressure of My electric fuel pump..
I'm now running a holley fuel pressure regulator..... and I haven't any flooding problems.... so the pressure is probably OK...
with a standard VW pump, there are many different thicknesses of Bakelite bases.... so the pressure between 2 cars can be different....
Maybe the pump is still putting out the same pressure but something else is causing the problem.....
Don't You just love VWs.....
You wouldn't have this much fun owning a Datsun would You??  :puke
Lee
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- [size=4]Helping keep Air Cooled VWs on the road - location: SCONE in the Upper Hunter Valley - Northern NSW 320 kms NNW of SYDNEY--- [/size]
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PurpleT3
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| posted on May 26th, 2005 at 02:18 PM |
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Just for future reference:
Density of petrol=737kg/cum
Max pressure of stock fuel pump = 4.5PSI (37kPa)
So:
If P=density x gravity x height
height= pressure/density x gravity
=37,000/737x9.8
= 4.3m
So you would need a tube at least 4.3m above the height of the fuel pump (if my maths is right)
I have seen Speco fuel pressure gauges on ebay for $40 ea, available in two ranges. I remember I had the pump out for a clean up and I might have
sanded the bakelite spacer to get the surfaces flat. So maybe, I have inadvertantly increased the outlet pressure of the pump.
Ain't nothin' like the wind in your hair.
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Andy
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| posted on May 26th, 2005 at 02:57 PM |
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I Tee'd a small VDO fuel pressure gauge into Andy's fuel line, was only ~$15 (few years ago now) and reads 0-15psi. Only about 30mm dia. so I leave
it there perminant. Stock pump on a type 4 (brand new Pierberg) puts out ~3psi.
ARE YOU GUYS"S SURE on adjusting pressure by varying the base block height?????
My experience shows stroke of the diaphram (varies with base block height, push rod length and wear on cam lobe) varies the volume pumped and the
spring under the diaphram sets the pressure.
This way the pump can put out a constant pressure, and vary the flow according to the needs of the motor.
:o
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PurpleT3
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| posted on May 26th, 2005 at 03:02 PM |
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I dunno, one of my service manuals says the pressure is varied by altering the distance that the push rod extends beyond the base block. Increasing
this distance increases the pressure and vice versa.
Ain't nothin' like the wind in your hair.
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Andy
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| posted on May 26th, 2005 at 03:06 PM |
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Cool
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PurpleT3
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| posted on May 26th, 2005 at 03:28 PM |
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I have managed to borrow a digital manometer, so I will try to measure the pressure. I can then vary the push rod distance by using thicker gaskets
and remeasure the pressure. I'll let you know what happens.
Ain't nothin' like the wind in your hair.
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