oh no!

My RB in my old car did that on #3. Pulled the heads..... nothing. Pulled the engine and stripped it down.... nothing. Honed the hole, threw it back together and raced it. Then one day it wouldn’t start. #3 again. Pulled the plug, cleared it out, raced it. Funny thing is that it wouldn’t do it all the time. Never polluted the oil... finally gave it a good dose of CRC Block Sealer. Lasted until I sold it years later.