Timing is a critical setting for Mercruisers or any other marine engine. Advance specifications indicate how much before (or after) the piston reaches total dead centre (TDC) that the spark plug should fire, igniting the air-fuel mixture in the cylinder. Firing too soon or too late will cause the engine to lose power and run inefficiently. Advance settings are usually expressed in degrees before total dead centre (BTDC) or after total dead centre (ATDC).
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Mercruiser 3.0-Liter Engines
The Mercruiser 3.0-litre engine should be set with a timing of 2 degrees ATDC. Timing order should be 1-3-4-2.
Mercruiser 4.3-Liter/V-6 Engines
The Mercruiser 4.3-litre and 4.3-litre H should be set with an advance of 10 degrees BTDC; the 4.3-litre EFI should be set at 8 degrees BTDC. All these engines should have a firing sequence of 1-6-5-4-3-2.
Mercruiser 5.7-Liter Engines
Mercruiser produced several models of these eight-cylinder engines. The 5.7-litre should be set with an advance of 10 degrees BTDC. The 5.7-litre EFI, the 350 Mag MPI, and the MX 6.2-litre MPI should all be set at 8 degrees BTDC. Timing sequence for all these engines is 1-8-4-3-6-5-7-2.
Mercruiser 8.2-Liter Engines
Mercruisers "big block" 502 Mag MPI timing of 8 degrees BTDC, and a firing sequence of 1-8-4-3-6-5-7-2.
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