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I have a 1972 Pontiac Ventura with a 307 engine. I swapped the stock 2 bbl carb and intake with an Edelbrock 1406 4bbl and airgap manifold (I saved the stock parts, don't worry). The cars manual calls for timing to be set at 8 degrees btdc but it seems to run better closer to 12 degrees or more btdc. Is it to be expected that the swap to a different intake and 4bbl carb would require more advance in the timing? Is there a way to adjust the timing by rpm to find the sweet spot since the factory setting doesn't seem to offer the smoothest idle?
 

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The stock timing is for a completely stock engine, and most likely has emissions in mind (followed by fuel mileage, with performance as the last thought). Lots of people would advance the timing on stock engines for more power at the loss of the other two.

Set the timing where you want it, set your idle speed, then adjust your carb, then idle speed and fuel again if needed. A vacuum gauge and tach make it very easy (for tuning purposes my tach is temporarily attached to the inner fender so I can do it without any helping hands).
 

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I would worry less about initial timing(timing at idle) and more about timing with the centrifugal advance all in. If you can mark the balancer at 40 degrees, Then check the timing with the engine at 3500 rpm (or wherever it stops advancing), you don't want to be over 40. I'd aim for 36 or 38 degrees. If it cranks hard when you start it hot, back some timing out. If after connecting the vacuum advance up it surges or misses while cruising 50-60 mph, you may have to back more timing out, or buy a limiter to limit vacuum advance.
 
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