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Old 05-20-2011, 01:50 PM   #1
Join Date: Feb 2011
Posts: 25
Ported to manifold vacuum conversion??

Alright guys so currently I have a ported setup on my 89 YJ with a HEI dizzy. It runs good now, but I would like to experiment with it on manifold vacuum. People seem to like manifold vacuum and I wanted to see what was so great about it. Only problem is when I tie into a port on the manifold the jeep stumbles and runs real rough at idle. My timing also jumps from 8* BTDC at idle(on ported / no vacuum) to around 22* BTDC at idle(on manifold). More advance is to be expected but with that much extra advance won't it be near impossible to get started? Once I give it some gas everything is fine because the manifold vacuum drops and the mechanical advance takes over. My question is how do I get it to idle right on manifold vacuum? Do I just need to lean out my idle mixture a bunch? Because leaner mixtures take longer to burn so with the extra advance at idle would compensate. (makes sense to me) I think I currently have my screws out 2.5 turns now on ported.


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