Just as one bad quarter doesn't mean a growth story is over, so, too, is it fair to say that one improved quarter does not necessarily mean that a story is back on track. So while I would expect to see more than a few optimistic headlines on Harley-Davidson's (NYSE:HDI) third quarter, I'm not going to sound an "all clear" just yet.

No doubt third-quarter results were better than what we've seen in the prior two quarters. Sales climbed 10% as the company achieved nearly 9% growth in motorcycle shipments. Margins improved with a better product mix and improved operating efficiency. Operating income increased by 16%, and product operating income increased nearly 20%.

Things looked generally all right on the product side. U.S. retail sales were up 12%, and sales in Europe and Japan also increased by double digits. Helped in part by six new models, the company apparently gained share across the board in all of its target geographic markets.

The finance side, though, is cause for a bit more concern. Operating income was down 5% as the company saw lower gains on securitizations of motorcycle loans. Not unlike what's happening with banks in the residential mortgage market, Harley is seeing its securitization spread squeezed by short-term rates that are rising faster than long-term rates. More worrisome, credit losses through nine months have climbed to 0.97 from 0.69. I'd suggest investors keep a close eye on this number as declining credit quality is seldom a harbinger of better performance.

All in all, Harley is a little tricky right now. On one hand, you have a solid and well-loved brand, and the company behind that brand is still producing a very respectable return on equity. On the other hand, you have declining credit quality in the finance arm, and dealers are increasingly lowering the premium they charge over the MSRP.

Making matters worse, I've got to think that Harley is going to suffer from the eventual end of the housing ATM. Some people refinanced their houses and put the money to work in stocks, investment real estate, or home improvement. But many others went to Best Buy (NYSE:BBY) for HDTVs, Coach (NYSE:COH) for expensive handbags, or their local Harley dealer for a hawg. Harleys are what you call an aspiration purchase. If the tap of easy money is being turned off, will there be enough well-heeled consumers out there buying enough bikes for management to hit its long-term financial guidance?

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).