originally it was a front intake engine with the carb just as you described. That didnt fit very well in my boat, and I had another K&B 3.5 with the exact same crank case but with a rear rotor carb. Well I took the front assembly off the front carb engine and switched it with the rear carb engine's front assembly. I then took out the front carb engines back plate and replaced that with the rear rotor carb. I can tell the carb is spinning and it is sucking in air when it is turned over. Like I was saying, when I cover the carb it sucks in fuel and runs until that fuel is used up. It just doesn't seem to be able to pull in the fuel by itself. I had this problem with the front carb and now the rear carb too. The rear carb seems a bit better but still no go! All the fuel line is new, just for an FYI