#1:"Quiet" Bakfire at idle #2: Vaccum Leak Fix?

[trndkll67]

1967 302 Mustang Coupe.

#1: So I was having a "quiet" backfire at idle(not a loud gunshot, just a soft intermittant 'pa-pop'), so I decided to pull off my Edelbrock card and rebuild it. The rebuild went great, and I reinstalled. But the backfire is still there. I twisted the Distributor a little to very the timing, but there wasn't much effect; the backfire was still there. I'm assuming it is a timing issue, but I not sure how to verify if that is the true cause. And I'm not really sure how to fix it. Any advice and/or specific instructions to fix would be greatly appreciated!!!!

#2: Also, the engine starts up fine with the new carb, but there is a lot of hissing, indicating an air leak. There is a vertical vacuum fitting the mounts into the intake manifold behind the carb. Two of the three holes have lines attached, but the third is open. There isn't any suction there, so I don't think this affects my leak. Any advice on how to isolate the leak, and where the leaks are typically located? Thanks!