XKE fuel pressure ?
#1
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I have 3 SD8 SU carbs on a 4.2 1970 E-Type, I installed a new (point type)
fuel pump from Barrett and noticed that sometimes the needles wood stick in one of the carbs causing that carb to flood over.
All 3 carbs had been carefully rebuilt with new SU kits and parts including new floats and float valves (not Gross valves).
Soooo... I went out and bought a 5 pound max pressure fuel gage and used it to test the output of the fuel pump. It read 4.9 lbs which is to high for normal float valves, so I installed an adjustable fuel pressure regulator, I set this to 3.6 lbs on the gage, which is what the SU instructions said should be the max pressure ! This has cured the problem..............but are all new SU pumps for XKE's putting out to much pressure ???
To answer this question I tested 3 pumps, all the same model, one used two new, all the pumps differed by as much as one pound (but within the advertised parameters) ! This is NO surprise given todays manufacturing techniques, the pumps are sold with a stated high and low limit in pounds per square inch pressure.
So what to do with a car that requires the lowest pressure rating on the pump you are buying ? You would have to test several new pumps (with an accurate gage) to get the one you want. Or disassemble a pump and shorten the spring to reduce the pressure ! The spring is what determines the output pressure of the pump. Conversely stretching the spring could increase the fuel pressure. What ever way you choose, you are going to have to test the output with a gage with the pump installed and connected to the carburettors to get an accurate reading !
I installed an adjustable regulator and a gage so I can always tell my fuel pressure.
fuel pump from Barrett and noticed that sometimes the needles wood stick in one of the carbs causing that carb to flood over.
All 3 carbs had been carefully rebuilt with new SU kits and parts including new floats and float valves (not Gross valves).
Soooo... I went out and bought a 5 pound max pressure fuel gage and used it to test the output of the fuel pump. It read 4.9 lbs which is to high for normal float valves, so I installed an adjustable fuel pressure regulator, I set this to 3.6 lbs on the gage, which is what the SU instructions said should be the max pressure ! This has cured the problem..............but are all new SU pumps for XKE's putting out to much pressure ???
To answer this question I tested 3 pumps, all the same model, one used two new, all the pumps differed by as much as one pound (but within the advertised parameters) ! This is NO surprise given todays manufacturing techniques, the pumps are sold with a stated high and low limit in pounds per square inch pressure.
So what to do with a car that requires the lowest pressure rating on the pump you are buying ? You would have to test several new pumps (with an accurate gage) to get the one you want. Or disassemble a pump and shorten the spring to reduce the pressure ! The spring is what determines the output pressure of the pump. Conversely stretching the spring could increase the fuel pressure. What ever way you choose, you are going to have to test the output with a gage with the pump installed and connected to the carburettors to get an accurate reading !
I installed an adjustable regulator and a gage so I can always tell my fuel pressure.
Last edited by felinecat; 02-12-2017 at 06:47 PM.
#2
#3
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Remember if one carb is leaking past the float valve this is reducing the pressure at the other carburattors so they are not likely to leak as well ! The length of the float contact arm and contact bearing as well as the floats being exactly the same volume all effect which carb could be flooding.
The rebuild kits were Burlen SUs
The rebuild kits were Burlen SUs
#4
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Feline, I have my 1970 etype coupe installed with triple su's for close to 28 years and drive my coupe close to 6,000 miles per year.
The pressure should be between 2 and 4 pounds.
If you want a life long fix and the car runs flawless......
Buy the airtex pump which came from a 1979 honda civic....
It fits in the same hole, hooks up to the same wires, doesn't tick and because it was for a Honda it will last longer than you!
Ive driven to Colorado, Indy 500 almost every year , florida , Daytona so every condition and altitude......the airtex is it, they are at EVERYparts store, they were around 30 dollars, now about 100 bucks and has a filter inline.....
You will never regret it.
The pictures say it all my friend.
GTJOEY1314
The pressure should be between 2 and 4 pounds.
If you want a life long fix and the car runs flawless......
Buy the airtex pump which came from a 1979 honda civic....
It fits in the same hole, hooks up to the same wires, doesn't tick and because it was for a Honda it will last longer than you!
Ive driven to Colorado, Indy 500 almost every year , florida , Daytona so every condition and altitude......the airtex is it, they are at EVERYparts store, they were around 30 dollars, now about 100 bucks and has a filter inline.....
You will never regret it.
The pictures say it all my friend.
GTJOEY1314
#5
#6
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baz I just checked, just type in airtex electric fuel pump for a 1973 to 1979 Honda.....
Everything is the same , they supply hoses and all, its soooo light you can put a spare in the glove box
Its 29 dollars and even has a new bracket as well.........
gtjoey1314
Everything is the same , they supply hoses and all, its soooo light you can put a spare in the glove box
Its 29 dollars and even has a new bracket as well.........
gtjoey1314
Last edited by gtjoey; 02-16-2017 at 06:11 PM.
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bazjag (02-17-2017)
#7
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#8
#10
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Remember this XKE thread is to inform and educate !
Their many electric fuel pumps that can be put on a E-Type BUT the recommended pressure is 3.6 pounds per square inch (4.2 engine with 3 2" SU carbs) in the last few threads we have owners talking about installing 4 to 5 pound pumps and even 5 to 8 pound pumps !!! This is way to much pressure and is high enough to overcome the float whose job it is to stop more fuel coming into the carb ! It is the design of the float needle area, the size of the float, the weight of the float, and the length of the float arm that determines when the fuel gets shut-off against delivery pressure ! This is how the engineers determined the IDEAL PRESSURE. Just because some owner goes out and buys an XYZ pump and it works like a charm on his car forever is no guarantee that the next pump purchased will have the same exact output !!! I have proved over and over again, by measuring the output of Jag SU pumps that their is NO consistency ! They are all different pressures...... The manufacture covers the inconsistency of the internal spring strength by stating the min and max of the expected delivery pressure. If you are fortunate enough to get a pump that delivers on the LOW end of the scale that will be fine. If you are like me and want to be sure use a gage (5 LBS max) and TEST THE PUMP!
Their many electric fuel pumps that can be put on a E-Type BUT the recommended pressure is 3.6 pounds per square inch (4.2 engine with 3 2" SU carbs) in the last few threads we have owners talking about installing 4 to 5 pound pumps and even 5 to 8 pound pumps !!! This is way to much pressure and is high enough to overcome the float whose job it is to stop more fuel coming into the carb ! It is the design of the float needle area, the size of the float, the weight of the float, and the length of the float arm that determines when the fuel gets shut-off against delivery pressure ! This is how the engineers determined the IDEAL PRESSURE. Just because some owner goes out and buys an XYZ pump and it works like a charm on his car forever is no guarantee that the next pump purchased will have the same exact output !!! I have proved over and over again, by measuring the output of Jag SU pumps that their is NO consistency ! They are all different pressures...... The manufacture covers the inconsistency of the internal spring strength by stating the min and max of the expected delivery pressure. If you are fortunate enough to get a pump that delivers on the LOW end of the scale that will be fine. If you are like me and want to be sure use a gage (5 LBS max) and TEST THE PUMP!
#11
#12
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You can keep the inline filter or remove as well....
I used fuel injection hose as the new gas eats through everything.
Next I used the filter and 45 degree fittings, this way the hoses fit perfect.
I double checked your new number, it is 2.5 to 4.5 lbs.
I just drove a wonderful 300 miles today in it. Went through mud and winery roads, will give it a bath in the spring.
I'm installing a DOUBLE PUMP positive ground in my ASTON MART DB2.
Believe me, if you saw this load, the airtex is a dream come true.....
Happy driving bench racers, see you at Indy, Import Carlisle , Amelia Island or Pebble Beach......Yes my ETYPE has driven to all of them from Ne York, with that one pump.......yawn.
Love you all
GTJOEY1314
#15
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Me and My friend Don as we drove from New York to Detroit for the filming of our tv show....FORD GT AN AMERICAN ICON, which you can all watch tomorrow on Velocity.
Same pump, 1, 500 miles in a 4 day weekend photo shoot at Rousch proving ground.
P.S. you are aware I'm filming at Amelia for our new show
LEGENDS OF DESIGN"ASTONS and JAGS"
D TYPES
XJ220;S
ETYPES
Mine with the same pump.
Are we getting the message yet yawn.....
Same pump, 1, 500 miles in a 4 day weekend photo shoot at Rousch proving ground.
P.S. you are aware I'm filming at Amelia for our new show
LEGENDS OF DESIGN"ASTONS and JAGS"
D TYPES
XJ220;S
ETYPES
Mine with the same pump.
Are we getting the message yet yawn.....
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