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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
| Posts: | 575 |
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1) When the car is parked nose-down on a steep hill with the tank/ fuel level above the carbs, the in-line anti-siphon check valve prevents fuel from flowing to the carbs, flooding them, perhaps to the point of over-flowing and causing a significant fire risk.
2) The fuel by-pass from the main output fuel line/ T-fitting back to the fuel tank, along with it's out-of-sight, 0.046" ID in-line restrictor orifice, functions as a "poor man's" dumb fuel pressure regulator. Under ONE set of factory-stock conditions, it bleeds off enough fuel to drop the stock fuel pump's "too high" output pressure down to the required ~2.5 psi measured at the carbs' inlets. Change anything, and the dumb regulator can't maintain the correct pressure.
For instance, install a different pump with a different output pressure, install it higher or lower in the car, or install a different fuel tank that somehow alters the elevation of the fuel mass relative to the carbs, and the fuel pressure at the carb inlet will change. The ‘dumb’ fuel pressure regulator can NOT preserve the correct fuel pressure in the face of change. Period.
If you make one of those significant changes to the fuel system (typically, an aftermarket fuel pump), then also delete the T-fitting, restrictor orifice, and bypass line back to the tank. Replace it all with an in-line, adjustable fuel pressure regulator, mounted as close to the carb inlets as practical, and set it to 2.5 psi.
When you're deleting all that stuff, be certain to keep the Anti-Siphon check valve.
Regards,
Tim Engel
Last edited on 02-13-2019 10:26 pm by Esprit2