Triumph Repair: 74 spitfire engine shut off

Question
My 74 spitfire will idle for approximately 30 minutes and then shut off.  I installed an in line fuel filter between pump and carb to observer fuel flow.  Engine stopped after 30 minutes and filter was empty.  After engine shut down, filter filled up but car will start and only run for approximately 3-5 seconds and then shut off again. Car will start up again after sitting for 30 minutes but the conditions repeat.  I have tested this condition with the tank cap open and results are constant.  There is an inline sensor/switch on lower radiator hose that several vacuum lines are attached but I cannot identify this part.  I was thinking that there is a vacuum issue but I do not know where to start the trouble shooting

Answer
Hi Terry,

The see through filter empty is a indication the pump has stopped pumping but to be sure you need to put a "T" at the end of the fuel line where it connects to the carburetors. Then put a hose to a fuel pressure gauge and watch the gauge when it dies. If the pressure dropped off of the 1.5 to 3 PSI BEFORE the engine dies then either the pump has failed or there is a stoppage in the fuel line to the pump. To confirm that you need to quickly remove the line from the tank at the pump and lower it down low to a pan to see if fuel runs freely out of it. If it does then the pump has failed it little to no fuel runs out then you have a partially stopped up line.

The later spitfires did have some emission items that can shut the fuel supply off in the jet of the single carburetor Spitfire by applying vacuum to the float chamber when the key was turned off but none of them have any vacuum that can shut off fuel to a fuel pump unless the charcoal canister transmitted the vacuum there to the fuel tank. But you eliminated that as a possible cause when you left the fuel cap off.

You need to quit looking for an item that is causing the cut off and only look at the system that is cutting it off.

Only 3 systems are required to have an engine run. Compression, Fire and Fuel. They MUST be tested in that order. Compression usually will not come and go and return like that so you can proceed to Fire (Ignition) It is easy to test if it is fire or fuel by just spraying starting fluid into the intake when it dies to see if it will start back up and keep spraying in the intake to keep it running. If you can't keep it running on starting fluid you have lost ignition. If you can keep it running on starting fluid then you have lost fuel. Then run the fuel gauge test I listed above.

Let me know,

Howard