hows the timing looking? also hook up a vacuum gauge and see what kind of vacuum you're pulling from the manifold.... and yes holley carbs crap out easy just like all carbs, if they sit too long or or get backfired thru, you'll probably be replacing parts.... with newer holley carbs they have a powervalve that doesn't go out from a single backfire now, but you can still toast your air filter, and then get bits of burnt air filter in your carb