Edelbrock 750......Vacuum Advance??

[coosawjack]

I have a 408W stroker with a Comp Cams XE-274H giving poor idle....I have to open primaries a little to get 950 RPM's!! Carb will not idle on the idle circuit!! BTW...Edelbrock says it should and they have some doing fine idleing at 8"...I have about 13" of manifold vacuum??

The Ford Ported vacuum advance unit on my Accel solid state distributor gives me full vacuum advance at idle since the ported vacuum reads 8" at 950 RPM's due to the idle setup!!

Mechanical advance is 24* all in by 3000 RPM's so with 12* base and 10* vacuum I have potentially 46* total especially if I try to use "Manifold Vacuum" side...

If I set the base timing at 12* with total mechanical of 24* and add "manifold advance" instead of "ported" I will have about 46* above 3000 RPM's cruising at 70 MPH!! I understand that acceleration will retard the timing with this setup but I'd much rather do it right!!

What am I missing here??

Thanks,
Jack

[dscott]

Jack, I usually don't use any vacumn on the distributor. I set the timing at 3000 rpm for 31 to 33 degrees and don't worry about the initial. If it starts and doesn't kick back it will work good. Some of the distributors from Ford are adjustable with an allen head wrench inside the vac pot. But as a rule they add too much advance. You also should not have any vacumn on the ported port at idle. You may be on the wrong one.
Don

[coosawjack]

Thanks for the reply Don.

I continued to fool around with it and by advancing the base to 15* was able to get it to idle on the idle circuit. With 24* of mechanical giving me 39* total at 3000 RPM's??

I think the ported vacuum only works momentarily when the primaries open and then drops back adding no advance at higher RPM's?? It really makes a difference in throttle response!!!

I backed the base back to 12* and it idles OK and max advance is 36* or so...Can't hear any detonation?? Side pipes are too loud!!

It was strong with no vacuum but it really is much better with it and I think it will be a little better on fuel??

Thanks again,
Jack

PS: How are you coming with CR II???