Idle air bypass

[camelracer]

I'm running a 327 SBC with a Quadrajet P/N 7044502 in a Jeep. I recently switched the vacuum advance from ported to manifold vacuum and now I can't get the idle speed below 800. I think I need to plug or restrict the idle air bypass. Will this be a problem with a low duration cam and if not do I plug the IAB in the carb body or baseplate?

[Zac Agee]

i would use the ported less timing at an idle and means lower idle speed. unless your cams big enough you need more timing at idle but your distributor hasnt been tuned for total timing. ported comes in just above idle so driving it you wont eaven notice the difference.

[camelracer]

The reason I changed to manifold vacuum was to lower the water temp while idling and help fuel milage. My previous worn out Quadrajet was a pre-smog ('68) and ran fine on manifold vacuum. The distributor is set up for 35* total advance plus 15* vacuum advance.

[Zac Agee]

running vacuum advance on manifold vacuum doesn't lower water temp when idling or does it make difference on the milage being ported comes in as soon as the butterfly's open hence right off idle its pulling full vacuum. there has been alto of posts on here on ported vrs. manifold and cliff will Even say use ported unless you have to use manifold vacuum. just trying to make something easier on you then more of a hassle is all not trying tell you how to you should setup your jeep

[TommyK]

To answer your question I don't think it makes any difference where you block off the air bypass as long as it is blocked off. You may however want to make it temporary because you may experience nozzle drip from having to open the butterflies more if the cam is big. You may want to see what size the bypass holes are now and figure out a way to re-size them smaller if temporarily blocking them causes you grief.

What is your initial timing now that you are hooked to manifold vacuum?

[Cliff Ruggles]

If the 327 has a small cam, and good vacuum at idle with "normal" spark advance, there is no need to give it any more advance at idle speed.  We very seldom use manifold vacuum to the advance for engines tuned here.  This assumes the cam is well chosen for the compression and CID......Cliff