Originally Posted by ggevaert
Wow, lots of discussion.
Thanks for the continued assistance;
Larger air bleed = leaner idle. If this is QF recommendations, I'd stay w/it unless the engine performance/plugs/a-f meter dictates otherwise.
As has been said already, use as much timing as the engine wants. The upper limit is determined by how it starts up, if it pings at throttle tip in (this will become more evident when the vacuum advance is brought on-line). But using the absolute maximum amount of initial timing isn't necessarily the best way to go about it. It is my opinion that using a medium amount of initial timing (which gives a broader amount of mechanical timing) should give better control of the spark timing over a broader range of engine rpm.
An example of this thinking is seen here
, where Demon carbs recommend 14-16 degrees BTDC for your engine/cam/carb size as a safe starting point. I'd recommend you work upwards 2 degrees at a time from there.
When it comes time to set up the vacuum advance, if for some reason you end up using 24-plus degrees initial, you may
find using ported vacuum better than manifold vacuum. Generally speaking, you won't need more than 10-12 degrees of vacuum advance.
More on timing is here
. The page is on GM HEI, but the timing info is relevant regardless of the distributor.
DO NOT be hesitant to readjust the idle mixture screws! They should be readjusted after just about any change made to the engine perimeters (timing, idle speed, plug heat range, idle air bleeds, etc.), and as long as the engine is fully up to temperature (fully- as in after a drive or a long
warm up if still undriveable), you cannot go wrong readjusting them as needed.