Tuning Guide

What tuning actually is

By Nathan Devonshire

Tuning has a reputation as a dark art. It isn’t. An engine tune‑up is two jobs, done in the right order — once the engine underneath is mechanically sound.

An engine needs three things

To run well an engine needs air and fuel in the right ratio, a spark at the right moment, and good compression to squeeze the mixture. Tuning is about the first two — the spark and the mixture. The third, mechanical health, is the foundation the other two sit on.

Mechanical health first — you can’t tune around a fault

This is the rule every good tuner starts with: a worn‑out engine cannot be tuned right. Burnt valves, wrong valve clearances, low or uneven compression, an air leak, a worn distributor, or — on a Stag — a cooling system that isn’t up to scratch, will all defeat you before you start. Sort them first, or you are building on sand. On the V8 especially, a healthy, correctly set‑up engine is a cooler‑running one, so tuning and temperature go hand in hand.

The two pillars

The spark (ignition)

The right spark, delivered to the right cylinder, at the right instant — the job of the coil, the distributor, the plugs and leads, and above all the ignition timing.

The fuel (carburation)

The right amount of petrol mixed with the incoming air, correct across every condition from cold idle to full throttle. On a Stag that is the job of the twin Zenith‑Stromberg carburettors.

Why the order matters

You set the ignition first, then the fuelling. How the engine sparks affects how it wants its mixture, but the mixture does not change the spark. Get the timing and ignition right first, and the carburettors have a fixed target to aim at; do it the other way round and you will chase your tail.

What ‘in tune’ actually gives you

A well‑tuned Stag starts promptly, idles evenly, picks up cleanly, pulls with that smooth V8 torque, returns its proper economy, runs at a sensible temperature, and lasts. A badly‑tuned one stalls, hunts, runs rich and hot, and fouls plugs — and does no favours to a cooling system already working hard. Much of the Stag’s unreliable reputation was really poor set‑up, not the design.

The Stag is made for this

Twin Zenith‑Stromberg carburettors and a distributor — no engine‑management black box — mean the whole thing can be understood and set up with a few tools and this guide. The following pages take each part in turn.