Hi Dave, I kind of thought the same thing, but one can't be sure. That's why I wonder if the back pressure might be high. Another concern I have is the seating of the carb on the engine itself. If there is a air-leak there it can have some really weird symptoms on the running of the motor. Another question that I think needs answering is, does the prop rotation of an engine being run in Austalia turn the same as in the Northern Hemisphere? I Know the water in the toilets turn differently. What do you guys think.....