Don't get your motors running just yet.

Harley-Davidson rumbled north on Friday amid dubious rumors that Honda was ready to purchase the motorcycle maker.

Shares of Harley-Davidson initially rose 6.3% but settled to a 4.2% gain, or $2.51, to $62.63 by noon trading.

However, despite the investor euphoria over the prospect of a Honda-Harley merger, there's a slim chance that Honda will follow through because of regulatory hurdles.

If Honda and Harley combined, the union would control 65% of the U.S. motorcycle market. The next leading competitor, Yamaha, would play a very distant second fiddle at 16%. That kind of stronghold on the motorcycle market would not please the Federal Trade Commission, which has squashed other, more innocuous mergers. Recently, the FTC rejected Whole Foods' bid to acquire Wild Oats because the arrangement would stifle competition in the natural and organic foods sector. (See: "Whole Foods' Wild Oater." )

"I'd be surprised if there was a Honda and Harley-Davidson combination, basically for regulatory and cultural reasons," RBC Capital Markets analyst, Edward Aaron told Forbes.com on Friday. "Harley is an iconic, American brand. I don't think it would be a great fit if they were under the ownership of a larger Japanese corporation."

Aaron also said it was unlikely that Harley would be the target of a leveraged buyout. "Although an LBO is more plausible than a merger with Honda, the math behind such a transaction is not highly compelling," he said. He then added that Harley is already a well operated business with a high margin profile and it would be difficult for an LBO investor to both pay a meaningful premium at the current price and generate a suitable return.

Investors may have been eager to ride the coattails of the Honda rumor because of Harley's lackluster performance as of late. Since November, shares of Harley have fallen 17%. In the first quarter, profits plunged 18% amid tepid sales and a three-week strike at a major production plant. While the strike was a negative one-time event, weak demand and an industry-wide slowdown was at the crux of the slip. Harley is also an unexpected victim of the subprime crunch, its financial services arm battered by higher defaults on its subprime loans.

------------------------------------------------------------------------------------------

By Evelyn M. Rusli