The aircraft collided with the ground after takeoff. The weather was VMC and no flight plan was filed. The aircraft was an amateur/experimental KR-1 with a VW 2100 cc engine, maintained under a condition inspection program performed by the owner. Investigation at the scene indicated that the aircraft impacted several trees at a moderate rate of speed and a steep approach angle. The aircraft had turned about 90 degrees to the left from the takeoff heading of 230 and came to rest 300 ft from initial impact. Investigation revealed that the aircraft carburetor had been replaced with another carburetor and the fuel line from gascolator to the carburetor made a sharp bend with a kink in the hose. The carburetor float was not of recommended size and some of the copper fuel lines from tank to carburetor had been cut with a tube cutter with metal extending over the holes, which had not been cleaned out. Three of the spark plugs would not fire at 120 psi; firing was normal when pressure was dropped to 100 psi.