power valve

Have a 680 quick fuel ss carb. I am wondering beings how these carbs have power valve blow out protection is it possiable for it to still happen? I had a back fire a few days ago while I was messing around and every since then my plugs foul really quick. I looked on summit and they are'nt very exspensive an i will probably change it just in case as it's cheaper then a set of plugs every 10 miles. I've driven the car a bit in the past an had'nt come across fouled plugs till the backfire. I think it ran a little rich before though. And the exhaust smelled alot like gas. But had'nt fouled the plugs till the backfire. I installed smaller jets in the front per quick fuel, for the altitude in Colorado, but with it fouling the plugs so quick It's hard to tell if it helped or not. When I installed the new jets in the front I was reseting the 4 corner screw in the same and I noticed that when I screwed in the drivers side all the way in while the car was running it did'nt stall at all. I did'nt try screwing them all in to see if it would die. But in the past if I screwed in the adjustment screws to far the engine would try and die. This is why I am leaning towards the power valve being out. I am hopeing I am on the right track, third set of plugs.