THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

I want to find out what fuel pressure is being delivered to my carbs because the car will not idle unless I keep the revs up. It starts fine on choke but when that clicks off, it wants to die. I have rebuilt the carbs several times and set them up as specified to no avail.

Keeping in mind that I want to keep the car looking as original, I'm not inclined to cut into the hard line from the pumps to the filter bowl in the engine compartment and install an adapter to accept the rubber hose on the tester, nor cut into the original plastic line from the filter bowl to the carbs. Maybe connect the tester back in the boot just forward of the pumps? That would require a connection at each pump.

Any thoughts will be appreciated. What is the recommended fuel pressure for the 3.8S engine?

I really think your issue is not with fuel pressure delivered by the pump. However, these pumps are designed to put out around 2.5 to 3 pounds of pressure. Much higher than that will overwhelm the float bowl valves and flood the carbs. If you are intent on measuring the flow and pressure from the pumps, (both pumps can be done separately), and not cut into the nylon lines leading from the pump the the front of the car, you need to order from Moss Motors, or elsewhere, this banjo fitting. Connect it to the output port on the pump, it is labeled, I believe, and connect a rubber hose to the banjo fitting and run it to a large jug and measure the flow. I am not sure the exact figure for the flow is but it should spurt continuously into the jug. Ensure the fiber washes are used and the banjo bolt is tight. You will need a Whitworth socket or box end wrench for this bolt. Here is the link to the Moss banjo fitting that accepts a rubber hose for testing.

https://mossmotors.com/c30946-banjo-fit ... t_products

John,

Thanks for the comments. Instead of pumping the fuel from the pump into a large jug and estimating the pressure, why not connect the rubber hose from my fuel pressure gauge to the banjo at each pump and measure the pressure directly? It would be nice to verify pressures if nothing else to eliminate that possible cause of my stalling at idle. Sounds like you have some other theories.

SInce you did not specify, does it do this on both tanks? if not then I suggest a clog in the pick up screen in that tank. Also, when it stops does it feel like its lean or rich? As much as I have leaned mine out, the car still leaves black soot on whatever is behind it where I park. Just throwing it out there......

awiedie,
You can certainly do the pressure measurement but keep in mind pressure is not the same as flow. Pressure created is built into the design of the pump with the diaphragm spring being the determining part. If the pump works, and it is the correct pump, I find it unlikely that pressure is an issue. More likely flow, which can easily be determined by the tube in the jug test. As stated, a clogged pickup strainer would impact flow. Someone may have a figure on what the flow is in 30 seconds or a minute.

Excellent suggestions John and Jerry. I must admit that the car sat for long periods between use, even after I removed both tanks and cleaned everything in the system. Not looking forward to dealing with all that gas again but maybe that's what I have to do. I guess I figured if the car was OK on choke, it must be getting enough fuel to idle correctly off choke.