Triumph Repair: engine running on, octaine, grade fuel

Question
Hi Howard
I have a 69 gt6, whenever I shut the car off the motor will continue to run on.  I have checked the timing 8 degrees btdc, and have put 94 octaine fuel in it although the car will run better with the higher grade fuel it does not stop the running on.  I have recently rebuilt the carbs, and put in new points, plugs etc.  I would appreciate any input that you could give me.  Thanks Stan

Answer
Hi Stan,
You should always run high test gas. As far as running-on after you turn the ignition off, there are several possible reasons.

You have already covered the fuel grade and timing but you need to look at float levels in the carbs. (17mm as I remember) What is your idle RPM? (750 to 850 RPM). Is there a sticker under the hood for ignition timing? (the sticker always over rides what your book says)
Is the engine overheating? Are you burning any oil? (oil has a very low octane rating and will cause "run-on")
A wiring problem can cause "run-on" too, allowing the charging system to feed the ignition after the switch is turned off. (easy to test by having someone turn the switch off at the same time you pull the coil wire off.) If it don't "run-on" then you have an electrical problem.
Let me know.
Howard