Triumph Repair: TR3A vapor lock, fuel pressure gauge, vapor lock

Question
I have a TR3A. The engine runs perfect, untill it gets hot, then it acts like it is starving for fuel and eventually dies. I have always been able to let it stand for a little bit and it will start up go for 1/4 mile and then die, thats how I get it home. tonight was different, it really had to cool way down. It runs perfect in the garage. I Restored the whole car except the engine. It had 68,000 miles on it, rebuilt carbs with new shafts and everything. new fuel pump and electronic ignition and new coil, and new timing chain. 70 lbs. oil pres. and 120 lbs. of compression so why rebuild it. I just can't figure this last little thing out. It only goes about five miles or so then it dies. I suspect a vapor lock. Any ideas on how I can remedy this.

Answer
Hi Mark,
You need to do some tests as what is suspect may not be what is wrong.
When I have a troublesome car that has an intermittent problem I divide the car into sections then divide that section into sections. I am often serprised what I find but never fail to find the problem.
You need to install a "T" in the fuel line close to the carb and run a hose to a fuel pressure gauge and run it out from under the hood and put it under a wiper arm so you can monitor fuel pressure at the moment of failure. (Be sure to put clamps on all connections
Also attach a timing light to a plug wire and tape the trigger down and tape it to the other wiper arm. (It is usually necessary to tape a piece of cardboard over the light end so you can see the flash of the light out in the daylight. Drive the car until it fails and look at both the gauge and the flashing light and you will be able to say, It is or is not ignition!! 100%. It is or is not fuel supply to the carb!! 100% (which includes vapor lock)
Once you have divided the problem into a "fore sure" category you make the next division. If it were an ignition failure move the timing light pick-up to the coil wire and repeat the test. If that dies too put a 12v test light on the power side of the coil and divide again. If it keeps the light lit move the test light to the negative side and repeat the test. (some test light bulbs draw too much current so here you may need an LED test light). (Radio Shack) or such.
If the fuel does die you need to wrap the fuel line that is from the tank to the fuel pump to see if it is vapor lock. The fuel between the pump and the carb is under pressure so much less likely to vapor lock. Raising pressure raises boiling point. Also remove the line from the tank to the pump and lower it into a can to see that there is a good flow of fuel. If a in-line filter has been added check it too. Run you test once with the gas cap open to be sure it is not a tank vent problem.
Let me know,
Howard