* TSX falls 99.19 points, or 0.80 percent, to 12,357.31 * Eight of 10 main sectors decline * Talisman drops after earnings report * Yamana Gold down 9 percent after profit drops * Tim Hortons jumps 4 percent after investor turns activist By John Tilak TORONTO, May 1 (Reuters) - Canada's main stock index fell on Wednesday, hurt by weak economic data from China that drove commodity prices lower and disappointing earnings reports from some of the country's biggest companies. Growth of the manufacturing sector in China, a big consumer of commodities which Canada exports, unexpectedly slowed in April as new export orders fell, raising fresh doubts about the strength of the economy after a disappointing first quarter. Investors were also nervous about an expected statement from the U.S. Federal Reserve later in the day and a possible interest rate cut by the European Central Bank on Thursday. Offsetting some of the weakness were gains in shares of Tim Hortons Inc, after a large investor called for changes, and in Loblaw Cos Ltd after the company reported first-quarter results. The Toronto market, which recorded its second-biggest percentage jump of the year so far on Tuesday, gave up some of those gains and slipped back into negative territory for the year. Miner Yamana Gold Inc recorded one of the biggest declines, falling 9 percent after reporting quarterly results, and the price of bullion weighed further as holidays in China and parts of Europe slowed gold buying. "Their results were lousy," said John Ing, president of Maison Placements Canada, of Yamana's first-quarter performance. "Higher costs were definitely a factor, but they were disappointing." He said the lower bullion price was hurting gold miners, which have lost about 35 percent of their market value since the start of the year. The Toronto Stock Exchange's S&P/TSX composite index was down 99.19 points, or 0.80 percent, at 12,357.31. Eight of the 10 sectors on the index were in the red. The materials sector, which includes mining stocks, declined 2.2 percent. Yamana reported a 40 percent drop in first-quarter profit late on Tuesday as lower gold prices and higher costs outweighed a boost in production. The stock was down at C$11.36. Energy shares gave back 1.7 percent as oil prices slipped. Suncor Energy Inc shed 1.6 percent and played one of the biggest roles of any single stock in leading the market lower. Talisman Energy Inc's shares fell 6 percent after the oil and gas company posted a quarterly loss as the sale of some North Sea assets hurt production. Tim Hortons has come under pressure from a large investor to aggressively boost returns through debt-funded share buybacks and a scaling back of U.S. expansion plans, according to documents seen by Reuters and two sources familiar with the matter. The stock added 4 percent to C$56.78. Shares of Loblaw jumped 5 percent to C$44.89 after the grocery chain reported a 40 percent increase in first-quarter profit and said it plans to compete the initial public offering of its real estate investment trust in early to mid-July.