The pilot reported that prior to the flight he removed an insulating blanket and heat source from the tailwheel equipped airplane, and conducted his preflight inspection. Following a normal engine run up, he initiated takeoff, where he thought the airplane seemed sluggish and that the rate of climb didn't feel normal. The pilot determined that the engine was not making full power, and decided to land at a nearby airport with a larger runway. Following an uneventful landing, the pilot diverted his attention to the engine instruments. Subsequently, the airplane swerved to the right, and the right main landing gear folded underneath the fuselage, which resulted in the right wing striking the ground. Postaccident examination of the airplane by the pilot revealed that the right wing spar was bent. The pilot added that he found an insulating cover over the carburetor air intake and that was the reason for the reduced power.