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'73 911 T Targa
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Is a return necessary in carb’d engine?
I’m replacing my tank, fuel pump and fuel lines.
Car was originally MFI, but converted to Webers by PO. Do I need to (re)install a return, or can I just use a single line and a pump with the proper pressure for carbs? |
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12-09-2023, 12:36 PM
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Registered
Join Date: Aug 2018
Location: Maryland
Posts: 2,264
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Not necessary, just a good idea.
Something about preventing vapor lock. If you don't have a return line then I would probably just run it as is.
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83' Coupe - Ex-RaceCar 77' Targa Narrow Body - SC powered Copper Brown Metallic |
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12-09-2023, 12:38 PM
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PCA Member since 1988
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Lots of old cars with carbs did not have return lines. You would need a pressure regulator with a return outlet.
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1973.5 911T with RoW 1980 SC CIS stroked to 3.2, 10:1 Mahle Sport p/c's, TBC exhaust ports, M1 cams, SSI's. RSR bushings & adj spring plates, Koni Sports, 21/26mm T-bars, stock swaybars, 16x7 Fuchs w Michelin Pilot Sport A/S 3+, 205/55-16 at all 4 corners. Cars are for driving. If you want art, get something you can hang on the wall! |
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12-09-2023, 04:53 PM
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The 9 Store
Join Date: Dec 2009
Location: Wilmington, DE
Posts: 5,341
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I was always told that carbs like cool fuel. A return helps that happen.
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All used parts sold as is. |
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12-09-2023, 05:17 PM
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It's a 914 ...
Join Date: Jan 2008
Location: Ossining, NY
Posts: 4,703
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It also depends on the fuel pump you use. If you want to convert a CIS car and use the CIS fuel pump (or an EFI type fuel pump), you MUST have a return line or you will overpressure the system and overwork the pump. A fuel circuit without a return line is sometimes called deadhead arrangement. With that kind of setup, an inline fuel pressure regulator will limit the pressure to the carbs so they'd probably be fine, but upstream of the FPR, very high pressure would build, which is hard on the pump, and potentially dangerous. Pumps intended for carb fuel systems are often designed accommodate such a setup.
I agree with mepstein's comments, but honestly for a street car it may not matter much. |
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12-10-2023, 02:36 AM
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Registered
Join Date: Dec 2014
Posts: 13,860
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Quote:
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12-10-2023, 06:02 AM
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Registered
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My $0.02 - Back when I had (non-P) cars with carbs, I always made sure that a return line with a fuel regulator was installed. This prevented vapor lock on hot days and seemed to help the bowl fill valve last longer (or it also seemed that way to me). I also felt like I was fiddling with the carb less after the return lines went in.
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12-10-2023, 06:32 AM
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