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Carb Model MA-4-5 Fuel Pressure Port

Zazoos

Well Known Member
I have Model MA-4-5 carburetor. The carb has a port for fuel pressure. My tempest fuel pump has a port for pressure. Other than the fuel pump being a bit closer to the firewall is there any reason why one port would be better than the other?

Thank you,
 
Is the port with the question mark meant for a fuel pressure line?

tempest-fuel-pump-left-side-lw15472.jpg


Thank you,
 
I say get from pump, the source, rather down stream at the carb.

In picture, Two sleeved lines are fuel into pump and out to carb, as Larry said other in picture, blue plastic is weep aka ...you got a problem if dripping. In my picture the black non sleeved line is going to my fuel pressure sender/transducer on firewall.
 

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Is the port with the question mark meant for a fuel pressure line.Thank you,
+1 that is a VENT LINE... not fuel pressure. Fuel pressure is typically plumbed via a "T" in the fuel line after the PUMP OUT before the CARB IN.

The Carb vent line is typically connected to short piece of tubing overboard. Inside the pump is a rubber diaphragm. On one side is fuel and the other is air. The vent is for the air side of the pump diaphragm. So this vent must never be blocked. It is unlikely the diaphragm will rupture, and the primary use is to keep the air side of diaphragm vented to ambient air pressure.

Fuel pressure:
In the old school days (still in use on older planes and war birds) an actual small fuel line was run into the cockpit to a mechanical pressure gauge that was read directly, no electrical needed. Now almost always we use an electric sender or transducer and run wires to the cockpit gauge which reads the variation in voltage as pressure. The electrical sender or sensor or transducer is typically mounted firmly on the firewall and a smaller flexible fuel line from the "T" is run to it. This keeps the engine vibration from affecting the sender, while keeping fuel outside the cockpit (verses the old mechanical fuel pressure gauge). It is good practice to put a small restrictor inside the "T" fitting so in case there is a leak it will reduce the volume of fuel leaking. The pressure sensor does not need volume to work only pressure, so a small orifice inside the fitting, much smaller than the hose, will suffice. There are a couple of ways to do this. You can buy fittings with a small 0.04 hole or modify a standard fitting using several methods, which the reader can research...

This is basic stuff. Check your Van's builders manual or Fire Wall Forward by Tony Bingelis
https://www.amazon.com/Firewall-Forward-Engine-Installation-Methods/dp/0940000938
 
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