On May 9, 2000, about 1245 hours mountain standard time, a Piper PA-18-150, N7345Z, sustained substantial damage when it lost power on takeoff and collided with a fence at the El Tiro Gliderport near Marana, Arizona. The Tucson Soaring Club was operating the local glider tow flight under the provisions of 14 CFR Part 91. The commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan. The pilot stated this was the 15th flight of the day for the airplane, but the first for him. When he relieved the previous tow pilot, he received a briefing, which noted the previous flights, airplane performance, and fuel status, 1/4 full in the left tank and a full right tank. He stated he was about 20 feet in the air while departing on runway 26 when the engine sputtered, regained power, then sputtered again. He released the glider and attempted to switch to the right tank. The airplane collided with a fence at the end of the field, bending the right wing strut. The glider pilot, who released about the same time as the pilot, landed off the runway in desert terrain next to the tow plane. A Federal Aviation Administration (FAA) inspector verified that fuel was in the gascolator, fuel lines to the carburetor, and the carburetor. He noted the airplane was equipped with a sight gauge in the wing root with a red ball in it to determine fuel level. Once the airplane was leveled and the wing placed back in its proper position, he observed the ball near the bottom of the sight gauge, which he estimated at less than 1/4 tank. The FAA inspector further reported that no fuel was found on the ground at the accident site. The original 150 horsepower engine was replaced by a 180 horsepower engine in accordance with Supplemental Type Certificate (STC) SA36RM. It stated the left tank was the main tank, which was to be used for takeoff and landing, while the right tank was an auxiliary tank, which was to be used in level flight only. This STC specified the original 3/8-inch fuel hose was to be replaced with a 1/2-inch fuel hose, but the FAA inspector noted this procedure had not been completed. However, an FAA office approved the operation of the airplane in the restricted category in this configuration, but only for the use of glider towing. The STC also required a placard be placed on the left (main) fuel tank noting "capacity 18 gallons, 9 gallons useable." Another placard, which read "EMPTY," was to be placed on the left-hand fuel gauge at the original 1/2 full mark. These placards were noted in a supplement to the airplane flight manual. This supplement also noted in the limitations section "Do not take off when left hand fuel tank gauge registers in the red area."