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Like rickm said, 9 degrees initial with the vacuum advance disconnected (the line plugged, engine idling at 750 rpm) are the factory specs.

I'd go a little further and ask you which heads the engine has and if there's been any "work" done (recurved distributor or aftermarket ignition, cam, etc.). For optimal performance, it's better (in my opinion, your mileage may vary) to set the "total" ignition advance at rpm (3000+) to what the engine "likes" and then let the initial timing just fall wherever it falls.

Bear
 

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Discussion Starter #4
the heads are stock stock carb petronex replacing the points i had a little backfire in exhust and advanced the timing and it seems better im waiting for the weather to clear and take it for a ride maybe tomorow and ill repost on how its running. engine is a matching number stock 400 350 hp
thanks tony g
 

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"Stock" doesn't tell us much. Sorry for not being more specific. We need the casting numbers off the tops of the center exhaust ports on the heads (usually 2 characters).
If they're open chamber d-port heads from the same model year (or close) then they're usually "happy" with around 34-36 degrees total by 3000 rpm. The closed chamber heads from 67 and earlier tend to like more - as much as 38 to 40 sometimes.

Bear
 

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If it's a stock 1970 GTO engine, I doubt very much that you'll be able to get away with 9 degrees initial timing on today's fuels. That is the spec for 100 octane fuel. You will probably have to set the base timing at about 4 degrees BTDC if that to avoid detonation.
 

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Discussion Starter #7 (Edited)
timing mark on balancer goes from 0 to 12 tried 9 and it backfired threw exhust so i went past 12 to what might be about 16 and seems to like it no backfire i will check numbers on manifold
thanks
 

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keep in mind, temperature, fuel octane, altitude, and the condition of the individual motor will alter timing. youl get it. i run sunoco 93 in n.y. and it seems fine.
 

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Backfire out the exhaust is usually rich mixture or burnt exhaust valves. Retarded timing causes backfire thru the carb, generally. Super advanced timing can cause a misfire/popping out the exhaust, too.
 
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