On October 2, 1993, at 1420 eastern daylight time, a Piper PA-28-140, N5695U, registered to Greenworld Liquid Fertilizer, and piloted by a private pilot, experienced a loss of engine power. The airplane collided with trees during a forced landing in Cheboygan, Michigan. The personal 14 CFR Part 91 flight was being conducted in visual meteorological conditions without a flight plan. The airplane was substantially damaged. The pilot and passenger both reported minor injuries. The flight originated from St. Ignace, Michigan, at about 1410 edt. The pilot stated he departed Livingston County Airport, Howell, Michigan, at 1015 edt, and arrived at his destination of Mackinac Island, Michigan, at 1235 edt. The pilot stated during a telephone interview that he estimated having between 21 and 27 gallons of fuel on board at departure. In the NTSB Form 6120.1/2 completed by the pilot, he reported having approximately 30 gallons of fuel. The pilot stated that he had planned to depart Mackinac Island the following day, October 3, 1993. Since no fuel was available at Mackinac Island he planned to stop at St. Ignace, Michigan, for fuel during the return flight. Upon arrival at Mackinac Island, he was informed that the runway at St. Ignace was going to be closed the following day. Therefore, he decided to fly to St. Ignace and refuel the same day. Upon arriving at St. Ignace, the pilot stated, he was informed that 80/87 octane fuel was not available, but that Cheboygan, which was a 10 minute flight away, had 80/87 octane fuel. Enroute to Cheboygan, while approximately 1 mile off shore, the pilot stated, the engine lost power. He stated he performed the emergency checklist which included switching fuel tanks, and the engine regained power. A loss of power occurred again after a few minutes. The pilot stated he elected to land in a wooded area as the only other terrain available was either water or heavily populated. The airplane contacted the tree tops and nosed down to impact with the terrain. Post accident inspection of the airplane by Federal Aviation Administration Inspectors failed to detect any fuel in the airplane. The pilot stated during a telephone interview that he elected not to refuel with the 100LL available at St. Ignace as he recalled being told that putting the wrong octane fuel in an airplane could cause engine damage. He stated he since had realized that he could have refueled with the 100LL without a problem.