Triumph Repair: 1974 spitfire 1500 fuel/carb, low pressure gauge, intermittent faults

Question
My Spitfire cuts out intermittently, sometimes my inline gas filter has no fuel in it. I suspected a faulty fuel pump replaced it and still have same problem. Investigating my sticky throttle I may have uncovered the problem but not sure, just behind the throttle spring there is what looks like a lever that pushes a small brass pin, it feels like the pin sticks or has a burr ( it clicks when I manually jiggle the throttle. What does this pin due, could it be source of my problem and is there a fix.

Answer
Hi Kurt,
If you are talking about a small pin that is moved into the case of the carb toward the air filter when the throttle is closed. That pin if sticking will hold the throttle open a little and must be free. It may require that you remove the carb and take the little "bell crank" with the adjusting screw off to remove the rod and clean it and the bore it is in. It runs almost all the way to the air filter. It is a vent valve but can not cause an intermittent cut out of the engine. Some times you can use something like WD-40 to spray on the pin and work it in and out to free it up without taking it apart.
An intermittent cut out is the most difficult to pin down because when you have the hood up and are checking things it may not act up. I designed a monitor just for that problem back in the early 80s when fuel injection was first being put on Import cars. I quit making them when ECUs started storing codes for intermittent faults. You need to do what I had to do prior to my fault finder.
At this point you don't have enough info to tell if it is ignition or fuel so put a "T" in the fuel line just before the carb. and run a hose out from under the hood and put a low pressure gauge (most vacuum gauges have a low fuel pressure section in them) under a wiper blade. Then get a 12 volt test light and attach it to the power side of the coil and run it out where you can see it. Run the car until you get the cut out and note fuel pressure and the light. If you have pressure and a light then you know it is not fuel supply and not loss of power to the coil. Then you connect a timing light to the coil wire in the center of the distributor cap and tape the trigger down if it is that type and place that under a wiper blade or tape it to a wiper arm. If it is a sunny day you may have to tape a piece of cardboard over the timing light so you can watch the flash of the light when you get your "Cut off". If you loose the flash when you have the cut off you now know it is in the ignition system so it is just a matter of going into the distributor and check each item.
All an engine needs is compression, fire and fuel to run. If you have an intermittent cut out, one or more of the three has failed. Compression will not come and go so it has to be fire or fuel. The tests above will narrow it to a small area so you can find it.
let me know.
Howard