i had the same prob and changed the clutch twice and three tob's. it is 99% your pilot bearing, i didnt change mine and did the same, now that you didint you should replace the tob and the pilot bearing together.
we just bought a 91 rx7 with a carbureted 13b(yes i know fuel injection is better), but it didnt come with a carb. we have plenty of them, but which is the biggest we could put on? we have a 1000cfm and a couple of 650cfm's.