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Registered
Join Date: Jul 2002
Location: Mercer, PA
Posts: 782
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And up from the carbs came some bubblin fuel
More Zenith carb problems. Tried to fire my 71' 911T and all was well until the fuel got to the carbs and the electric pump didn't shut off. I went to the engine and fuel was bubbling up from the carbs-good flow I might add. I'm thinking stuck floats....anyone, anyone, bueler,bueler..
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07-13-2002, 07:17 AM
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Senior Member
Join Date: Jun 2000
Location: N. Phoenix AZ USA
Posts: 28,943
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One, you need to confirm that the float valves do shut off the flow of fuel. Also, are you positive that the fuel pump is the correct pressure?
If the float valves do shut off the fuel flow its possible that the pump is too high a pressure version (have seen a fuel injected pump being used on a carb car and it pushes way too much fuel) and "overpowering" the float valves. You can always do a "flow check" and see how much volumn it is pumping as well as check out the pressure. Joe
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2013 Jag XF, 2002 Dodge Ram 2500 Cummins (the workhorse), 1992 Jaguar XJ S-3 V-12 VDP (one of only 100 examples made), 1969 Jaguar XJ (been in the family since new), 1985 911 Targa backdated to 1973 RS specs with a 3.6 shoehorned in the back, 1959 Austin Healey Sprite (former SCCA H-Prod), 1995 BMW R1100RSL, 1971 & '72 BMW R75/5 "Toaster," Ural Tourist w/sidecar, 1949 Aeronca Sedan / QB |
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07-13-2002, 07:36 AM
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Join Date: Jul 2002
Location: Mercer, PA
Posts: 782
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I think you've hit the nail on the head. I'm thinking that the person that decided to make changes did so ill advised and may have been trying to get more out of the car than it could give. only have the Haynes manual and the Zeniths don't look too bad to take apart and I'll start there, but I know from when I got the car the carbs where a mess but it ran and didn't have this problem. I'm thinking 3 years of reconstructive surgery and a lack of foresight on my part-to fogg the carbs, may have led to this, but I have receipts showing a new fuel pump so........
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07-13-2002, 01:32 PM
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Join Date: Jul 2001
Location: Woodbine, Maryland USA
Posts: 251
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Allen
Does this car have the OEM Bosch fuel pump? If so, is the return line from the fuel pump connected to the metal return line exiting through the firewall? The return line keeps fuel pressure at the carbs constant. When fuel pressure reaches a prescribed cutoff limit (needle valves shut off fuel at the carbs), the return line dumps excess fuel back to the tank, thereby bleeding off pressure at the needle valves. The return line is activated by a switch in the fuel pump when pressure in the delivery line reaches (if I remember correctly) 2.8-4.2 lbs. of pressure. If the return line isn't connected, the pump will overpower the needle valves. I'll check my spec book when I get home and check to see if my memory regarding the pressure at which the return line activates is accurate. If not, I'll post with the accurate info. Good luck.
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John 1972 911T Coupe PCA- Potomac Region |
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07-14-2002, 06:27 AM
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Join Date: Jul 2002
Location: Mercer, PA
Posts: 782
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This is exactly the info I need. The Fuel pump currently in the car does not have return line and the metal line thru the fire wall is not connected. Actually, there is no return line exiting the carbs so I need to know where one would connect. Evidently if there use to be one, it must have been plugged at the carbs and I can't tell where it went. I think the pump is overpowing the carbs but I may take them apart to see if the floats are funtional, but not till I get all the lines properly attached. Thank you very much for the info all ideas are welcome.
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07-14-2002, 08:07 AM
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