Triumph Repair: 76 Spit runs rough when engine gets hot.

Question
I've had a 1976 Spitfire since 1979.  The last couple of years when the leisure driving season begins, my Spit will start and idle fine.  It will run OK until the engine heats (2-3 miles) up and then runs very rough, spits and may even stall and will not restart for 10-15 minutes.  I've read something about a fuel vapor lock??? Have taken it to a Knoxville, TN British repair guy but the problem continues.  Can't use the car in this condition. Frustrating.  HELP!!!!!
Thank you

Answer
Hi Richard,

Your repair man may have missed the fault due to testing when the problem is not there. An intermittent fault is the most difficult fault to locate.

Although symptoms can sometimes lead you to a fault they are usually useless. Testing is the ONLY method to locate a fault and an intermittent fault MUST be tested in it's failed mode. (when it is failing#

Here is the sequence of tests you must run. Run a compression test #Cold) then heat the engine up to operating temperature and run the compression test again. You should see from 135 PSI to 180 PSI on all 4 cylinders cold and hot with very little difference between cylinders.

Next, connect up a fuel pressure gauge to a "T" placed in the fuel line just at the carburetor. (be sure to put clamps on all joints) Use a long hose on the gauge and place the gauge under a wiper arm so you can view the reading while driving. (careful not the cut the hose where it comes out from under the hood) Pressure should be from 1.5 PSI to 2 PSI while driving hot.

The ignition test can be done at the same time by placing a timing light on the coil wire and tape the trigger down so the light is flashing all the time. Now place the timing light under the other wiper arm so you can see the flash while driving. On brighter sunny days you may have to tape a small piece of cardboard over the light end to shield the sun light so you can see the flash of the timing light while driving.

These tool are necessary and are not expensive and can be used on any car later if you don't already have them.

These tests will confirm the engine is good cold and hot and is or is not the problem. The fuel pressure test confirms fuel supply to the carburetor during the failed mode which eliminates the fuel pump, lines and tank as a cause. The timing light will confirm ignition at the time of failure thus eliminating the ignition system.

Compression, fire and fuel are the only systems necessary for an engine to run. When you ID the system that has failed, it is then easy to find the actual part that failed.

Let me know,

Howard