Well...I replaced my flywheel and I still have the rattling on shutdown. The opinion seems to be the car is 'dieseling', still kicking after the ignition is shut off which is a timing issue apparently.
It's amazing how many issues aren't noticed when the engine is mated to an auto, but rear their heads when a manual box is bolted up...
Potential causes Of Dieseling
This condition can occur for a multitude of reasons:
Built-up carbon in the ignition chamber can glow red after the engine is off, providing a mechanism for sparking unburnt fuel. Such a thing can happen when the engine runs very rich, depositing unspent fuel and particles on the pistons and valves. Similarly, non-smooth metal regions within the piston chamber can cause this same problem, since they can glow red. It has also been suggested that an improperly rated spark plug can retain heat and cause the same problem.
A carburetor that does not close entirely can contribute to running once the engine is off, since the extra fuel and oxygen mixture can combust easily in the warm piston chamber. Similarly, hot vaporized oil gases from the engine crankcase can provide ample fuel for dieseling.
Incorrect timing.
An engine that runs too hot or too lean may produce an environment conducive to allowing unspent fuel to combust.
An idle speed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turnover and combust more fuel and lock itself into a cycle of continuous running.
Thought this might help
