Hi, I was going to replace the power valve in the teapot carburater for a 53 Merc flathead. After taking it out, and bringing to a couple of local parts stores, all they had available, and what shows from Holley is a power valve that looks like a bolt with a large nut on top. Mine looks like a bolt with the plunger in the center. To any event, I removed the gas inside, removed float, spring to access and clean because of dirt on the bottom. After reassembling, the cars runs really rough. After tightening all screws, cleaning, could this affect the timing? There's no backfire. I have the float and float spring installed correctly, along with the seat and needle. A head scratcher.