Ok, check this out...I had a sputter and power problem with one of my kits as well. It ran great for the first week and then all of a sudden no power, sputter, 20mph top end etc.... I finally figured it out after 2 carb's, new wire and end, new plug, new CDI, new rings and all. Here is what caused my problem and once done I am riding SMOOTH once again.
The problem was restricted Air/Fuel flow to the cylinder by the factory intake gasket. It seems the gasket is cut to the size of the intake and not the cylinder. Once the gasket was saturated with fuel and oil it expanded and interfered with the flow.
The fix: Remove the carb and intake. Cut the intake gasket center hole out using the engine side as a guide (I used an exacto knife). Be careful not to get pieces in the engine. Add blue sealer (small amount) to both sides of gasket and re-install. Mine runs GREAT now.
I hope this helps. Let me know if anyone needs further info on this such as symptoms,or fix procedures. I love it when a plan comes together!
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