I have a 1970 440 6-pack set up. Center carb was leaking so I took off and had rebuilt. No leak now but backfires at low speed. The place that rebuilt it does put it on a engine and fine tune it. One thing I did notice when I got it back was the nipple which was plugged when I got it back was the lower one. When I took it off before having rebuilt the upper nipple was plugged. I believe the black hose connected to it is a vacuum line see picture
Anything else I should check. Car was not backfiring before rebuild by highly recommended shop.
Attachment 8188
Anything else I should check. Car was not backfiring before rebuild by highly recommended shop.
Attachment 8188
