picked up a Chevy 350 for 4grand recently came with dyno sheet 390hp since the first time it fired it has run rich, rich enough to foul plugs. It has a 600 cfm qtf slayer carb, now, the float levels stay dead center had one test run, seems to run rich all the way through the circuits, at idle it acts like it loaded up till you rev it a couple times then it smooth's out for a few seconds. does this sound like power valve issue's, only thing I changed was to add a 1,1/2 spacer. It is under warranty but the truck isn't ready for the road yet. I'd just like to get an opinion on what could have went wrong, it runs rich even with the break vacuum opened. thanks