The Tuning Guide
Tuning the T-Series: the complete guide
Tuning a classic engine sounds like a dark art. It isn't. Strip away the mystique and it is two jobs — getting the spark right, and getting the fuel right — done in the right order, with an understanding of what each part is actually doing. This guide explains all of it from first principles, with the specifics of the MG's twin SU carburettors throughout. Read it start to finish, or dip into the part you need.
The full set is now live: the fuel side and every ignition page, ending with a step-by-step setup for the twin SUs. Read straight through, or jump to what you need. More marques will follow in their own guides.
Start here
What tuning actually is
The two jobs an engine tune-up really does, the order to do them in, and why mechanical health comes first.
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The fuel side
How a carburettor works
From the venturi upwards — the two families of carburettor, and exactly how the MG's twin SUs meter fuel.
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The ignition side
How a distributor works
Points, condenser, cap and rotor — how the spark is triggered and delivered, and how the advance works.
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The ignition side
Ignition timing explained
Why the spark fires before top dead centre, and how to set timing statically and with a strobe.
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The ignition side
Spark plugs, coil & firing order
The rest of the ignition system: how a spark plug fires and how to read one, the coil and ballast, HT leads, and the 1-3-4-2 firing order.
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The fuel side
Setting up the twin SUs
A fixed sequence, done in order: float level, jet centring, balancing the pair, mixture by the lifting pin, and idle.
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The specialist
This guide is illustrated with thanks to Andrew at AG Classic Car Tuning, a North Yorkshire mobile specialist in the carburettor-and-distributor classics of the 1930s to 1990s — SU, Stromberg, Weber and Solex — who tunes these cars for a living.