holley hell

In answer to your questions;
1) Most certainly your float level is too high and/or your needle is leaking. Quick way to tell: pull the sight plug off the side of the float bowl. The fuel level should come up to the BOTTOM of the sight plug, just to the point where it dribbles out a little. To my knowledge, the 4160 float is adjustable unless they've changed something? If you can snap a pic of the carb and post it, I can walk you through it; I ran a 4160 on my Duster and was able to adjust it with no problem????
2) Yes, they DO have a power valve and yes, a backfire WILL blow it out and make the carb run super-rich; i.e. the engine will run like crap. Summit sells replacement "blow-proof" power valve kits; HIGHLY recommended. Any other questions and/or comments, please let me know.