Shares of Harley Davidson (NYSE:HOG) have run hog wild, up almost 50% since last June. From an investment standpoint, is now the time to pack it in? Or should we keep it on full throttle going forward?

Today Harley reported fourth-quarter and full-year 2006 earnings. Our recent Fool by Numbers will ride you through the quarterly details: for the year, total sales grew 8.6%, net income grew 8.7%, and diluted earnings grew 15.2%, as management repurchased over $1 billion in company stock. The overall performance was not terribly impressive, but sales growth accelerated slightly toward the end of the year and the company is bullish on its prospects for at least the next couple of years.

Harley believes it can increase earnings at an 11%-17% annual clip through 2009. That's below the 22.5% annual earnings gains it has reported on average over the past five years, as growth has slowed in recent years. And while the earnings projection enhances visibility over the next three years, the range is wide enough to allow management some leeway, should growth fall back toward the single digits as it did from 2005 to 2006.

Currently, shares of Harley Davidson are trading at just under 19 times trailing earnings and just under 17 times consensus estimates for 2007. That's not overly high for a company with a stellar, two-decade track record of steady growth, and it looks to be a very reasonable multiple should earnings growth come in at the high end of the expected range.

One concern I have is that operating cash flow came in well below reported net income for the full year, something that last occurred in 2004. I'll wait until the annual 10-K is filed for more details on why this happened, but at worst it means that inventory is rising and earnings quality is deteriorating as the company is stretching to keep growth chugging along. I'm not saying that is the case, but the lower cash flow generation is something that warrants further explanation.

It also remains to be seen how widely Harley motorcycles will be embraced outside of the core U.S. market. Domestic growth is clearly slowing, as illustrated by fourth-quarter trends that saw sales growth of only 0.3% at home and 29.4% overseas. It's too early to tell if the bikes will experience the same baby-boomer popularity in other markets as here at home, but so far so good. However, with less open roads elsewhere, smaller bikes -- such as those sold by Ducati (NYSE:DMH) or Honda (NYSE:HMC) -- may be the way to go.

In any case, Harley is a very profitable company and has plenty of capacity to benefit shareholders by raising its dividend and buying back stock. Growth trends are unlikely to return to the firm's heyday in excess of 20% annually, but there is still room for this American icon to run.

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Fool contributor Ryan Fuhrmann has no financial interest in any company mentioned. Feel free to email him with feedback or to discuss any companies mentioned further. The Fool has an ironclad disclosure policy.