This may sound like a strange question, but... when I bought my 84 GSL it had the original exhaust and muffler. It would also flood about 60% of the time it rained. If it was raining all day I knew the car wouldn't start because it was flooded. When the original muffler fell off, I replaced it with a cheapie Cherry Bomb. After that it didn't flood any more. I recently replaced the entire exhaust and had a new (but original) muffler put on. The one with the dual tail pipes. Lo and behold, it started flooding again. Could there be any correlation between the two, or is this just a coincidence?

 

sounds like you have a vaccum leak. when my car used to do that, i replaced my aab hose and bam. never happened again. check it.