Quote:
Originally Posted by Jac Mac
Vac advance on comes into effect at cruise/part throttle mode, however if its hooked up to wrong port on carb it may be getting full advance at idle & if your $400.00 mechanic did not realise this and set advance at idle with it connected your car will not be getting full advance on the road under power. Disconnect & plug advance tube then check ignition timing at idle ~10°/12° should get you started, then run up to ~2500+ and check your getting something like 30°/35° total advance to check dizzy mech advance for starters.
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Correct - disconnect the vacuum hose from the distributor and plug it before checking timing, then un-plug it and re-connect it once your idle and total timing has been set.
BTW, there has been much confusion over manifold vacuum vs ported vacuum, with people in both camps. After spending way too much time digging in to this issue it became apparent to me the use of ported vacuum started at the beginning of the emissions era and is not suitable for most engines in Cobras. I'm firmly in the manifold vacuum camp, that's what I'm running on my BBF and it seems to like it - the idle is smoother and the idle speed increased about 150-200 RPM after hooking up the vacuum advance to full manifold vacuum.
Ported vs Manifold vacuum:
Carburetor Question - Vintage Mustang Forums
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