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I've got a question about my 1985 454 Mercruiser engine. I'm trying to adjust the timing but when reading through the engine manual it sounds like it's giving contradicting information.

On page 27 is states: Timing (at Idle rpm) 8° BTDC

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On page 354 it states to manually adjust the engine throttle to 1800 rpm + 200 when checking timing (see number 3).

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This is the document I'm reading: https://d3gqux9sl0z33u.cloudfront.net/AA/AR/wetbristol/downloads/224953/Mercruiser_v8_7.4_8.2_litre.pdf

Should I check my timing at idle (which is ~750 rpm) or at 1800 rpm? Appreciate the help!

1 Answer 1

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There is an annotation on the page 27 entry stating you should follow the special instructions for setting timing. This involves putting the ECU into a special mode. When this happens, set the RPM to ~1800 (+/-200). When you take it out of this mode, set the engine back to idle (~800 RPM), you should be able to check the timing and it should be 8° BTDC. IOW, one (pg 27) is to check the timing to ensure it is correct, the other (pg 354) is for setting the timing.

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