I just replaced my entire fuel system plumbing from the gray lines to new ones. I have one carburator. It was not necessary to take the carb off of the engine in order to get at it and do what needed to be done. I took the cover and block off and cleaned the black junk off of the tiny filter that was in that location. I tried to be careful not to puncture or tear anything like he diaphram or the clear celophane looking thing that was on one side of the block. I also cleaned the main fuel filter with soapy water but it wasn't too bad to begin with. I sprayed the selector valve, carb and inlet tubes with Gumout (before reinstalling the tiny filter.) I added one container of carb/fuel injector cleaner additive to gas tank. The engine started right up and idled fine. I had the garden hose attached to the backflushing fitting (without the exit side pinched off) to cool it with water sufficiently while I searched for leaks. No leaks were found. I started to slowly accelerate the throttle. At about half throttle the engine seemed to reach its max power and would not produce any more. As I continued to increase the throttle to full speed I started to encounter backfiring. It only did this when I maxed out the throttle. While I had the engine apart I did not touch any settings or mess with anything. I just took off the carb cover and block to get at the filter and replaced it when I was done. The backfire seems to be a loud puff of air in the large steel muffler looking thing on the back left side of the engine compartment (I don't know what this thing's name or function is) and did not seem to originate in the carb. The plugs are brand new and it was not backfiring before I changed the fuel lines. What could be causing this and how do I fix it? Thanks 
Dean
Cincinnati, OH
Dean
Cincinnati, OH
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