BusinessWeek reports that Thomas H. Lee Partners LP agreed to acquire CKE Restaurants Inc., owner of the Carl’s Jr. and Hardee’s fast-food chains, for about $619 million in cash. The shares jumped the most in almost nine years in New York trading.

CKE investors will receive $11.05 in cash for each share of CKE common stock they hold, the companies said today in a statement. That’s 24 percent more than yesterday’s closing price of $8.91. Thomas H. Lee also agreed to assume about $309 million in debt for Carpinteria, California-based CKE.

“It’s a fantastic company that produces a lot of free cash flow,” said Mark Smith, a restaurant analyst with Feltl & Co. in Minneapolis. He recommends holding the stock, which had climbed 28 percent in the past year before today. “They weren’t out looking and begging for a buyer,” he said.

CKE had free cash flow — cash flow from operating activities minus capital spending — of $11.5 million in the third quarter, more than double the average of 50 restaurant companies, according to Bloomberg data.

Sales at CKE restaurants open at least a year fell 6 percent in the quarter ended Jan. 25, as unemployment remained high and competitors lowered hamburger prices, the company said this month.

The stock jumped $2.25, or 25 percent, to $11.16 at 10:30 a.m. in New York Stock Exchange composite trading after reaching $11.24, for the largest intraday gain since April 2001.

Industry Pioneer

CKE has 3,147 restaurants in 42 states and 14 countries, including 1,221 Carl’s Jr. restaurants and 1,913 Hardee’s. Founder Carl Karcher borrowed $311 to buy a Los Angeles hot-dog cart in 1941 and became a pioneer in the industry, introducing salad bars, char-broiled chicken-breast sandwiches and self- service beverage stations. He died in 2008.

Thomas H. Lee, which also owns a stake in Dunkin’ Brands Inc., operator of the Dunkin’ Donuts and Baskin Robbins chains, has raised $22 billion of equity since its founding in 1974. The Boston-based firm, also known as THL Partners after founder Thomas H. Lee left the company he founded, has invested in more than 100 businesses with an aggregate purchase price of more than $125 billion.

CKE has through April 6 to solicit better offers from third parties, according to the statement. The deal values CKE at about 12.5 times earnings over the next year, below the 14 times average of other fast-food restaurants, Smith said. Barring other bids, the deal should close in the second quarter of this year, the companies said.

UBS Investment Bank and law firm Stradling, Yocca, Carlson & Rauth are advising CKE. Bank of America Merrill Lynch and law firm Ropes & Gray are advising THL.