Triumph Repair: wants to keep running after the key is off, manifold vacuum, vacuum hose

Question
what is causing my 1972 spitfire to diesel , and second is it common while the engine is running if you take off the oil fill cap on valve cover the engine dies.  

Answer
Hi Jeremy,
The two problems may be related. It sounds like you have your manifold vacuum connected directly to your crankcase vent. Some British cars did have vacuum routed to the crankcase but not full vacuum and I don't think the 72 Spitfire did that. This takes oil fumes into the combustion chamber and burns those vapors which have a very low octane rating and can cause detonation (dieseling)

First check the routing of the crankcase vents and vacuum hose routing.

Howard