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TOPIC: 1970 Merc 500 Timing Question

1970 Merc 500 Timing Question 2 years 6 months ago #128341

  • riceman
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Hi all -

I am going through my 1970 merc 500 (with electric start) and am at the point that it's ready to set timing.

The manual I have from boatinfo ( boatinfo.no/lib/mercury/manuals/mercury_1965-1989_40-115.html#/4 ) says that mine is required to be running to set timing. Idle isn't a real issue to set the base timing, but it also says that I need to be running under load at WOT in order to set the max timing advance. This sounds pretty sketchy to me as I don't have any desire to be hanging off the back of the motor running down the river at 20-30mph trying to set the timing.

i know it's a completely different motor, but my buddy's 2004 mercury has you set the timing while turning the motor over with a key and the spark plugs removed, so...

my question is: since the advance mechanism is completely mechanical, is there any reason I can't do this with my motor? is there something special about the motor actually being running at idle and WOT?


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Re:1970 Merc 500 Timing Question 2 years 6 months ago #128343

Chris, I did my 71 500 with the plugs out and spinning on the starter. Throttle manually set to WOT and then adjust the timing adjust stop. You are absolutely correct, there is no way to do it with the engine actually running under load. Idle timing no problem. Make sure your plugs are able to spark. I drilled holes in a flat piece of aluminum (4) and screwed the plugs in. A ground wire from the aluminum to the block and you are good to go.

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Remember, my opinion in no way diminishes your opinion, nor yours mine. Collectively, there is a middle ground that is \\\"correct\\\" for the reader balancing all the input.

Re:1970 Merc 500 Timing Question 2 years 6 months ago #128345

use a test wheel. short of that either tie the boat to the dock or back it in to the ramp on the trailer leave it on the trailer, disconnect the carb pickup so you can advance the mag without moving the carbs. then use a timing light and advance the mag and set.

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