The Triumph TR6 was the pride of the British Leyland Motor Corporation with its in-line six-cylinder engine, disc brakes and advanced independent rear suspension. The sporty little TR6 package was rounded out with rack and pinion steering, bucket seats and sport instrumentation. When in tune, the TR6 is a powerful and fun car to drive. Problems with an engine backfire rob the car of its performance and fuel economy. Diagnosing and repairing a backfire is an easy task that lies well within the ability of the average weekend mechanic.
Set the spark plug wires to the following firing order: 1-5-3-6-2-4 counterclockwise, with the #1 cylinder at the front of the engine.
Set the ignition timing. Connect one end of a 12-volt, 21-watt lamp to the coil's low tension terminal. Connect the other lamp lead to the battery's positive (+) terminal. Rotate the crankshaft pulley until the indicator hole on the pulley is exactly 3/8-inch to the left of the timing pointer. Turn the distributor until the lamp just comes on. Tighten the distributor and remove the timing lamp.
Check the vacuum retard on the distributor to ensure it is connected to the correct vacuum source. Check all other vacuum hoses for loose or cracked connections.
Adjust the ignition point gap to .015. Inspect the points to ensure they are not pitted or burnt and that the spring is functioning correctly.
Adjust both ZS carburettors to set the idle speed at 900 RPM. Using the special synchronising tool is the preferred method and the most accurate, but the adjustment can be done with a common vacuum gauge if a synchroniser is not available.
Adjust the valve clearance on all cylinders to .010-inch.
Check the wiring harness for loose connections or broken earth straps. Repair as needed.
A fender cover or old blanket will protect the finish of the car when working under the bonnet.
Use wheel chocks and set the parking brake to avoid unexpected vehicle movement.