Charles Portis is back with another novel, his fifth. For Portis fans that's good news. It would be better news, though, if the book were better - and the book's not bad.

That's the continuing problem for Portis. He had the bad luck of writing an American comic classic - "True Grit" - early in his career, and everything he's done since then has had to be judged against it. Joseph Heller and J.D. Salinger no doubt know the feeling."Gringos," the new book, has in it a lot of what readers have a right to expect from Portis. It's funny, quirky, full of offbeat characters and involves a chase. This time the story is set in the Yucatan, and the point-of-view character is Jimmy Burns, a former Mayan-tomb robber trying to go straight now in a society of marginal expatriates (the "gringos" of the title) that doesn't exactly encourage this.

Everyone has too much time - and too little money. The chase involves a runaway girl from the states who has taken up with a band of mean hippies intent on staging a sinister new-age happening at one of the local pyramids. Burns, who makes part of his living rounding up such runaways for the fees offered for their return, attempts to retrieve the girl, LaJoyce Mishell Teeter, even though she doesn't particularly want to be retrieved.

All of this is OK, but it suffers in comparison to the high comic melodrama of the chase scenes and conclusion to "True Grit," with its quick reversals of fortune, its pit of snakes and so on. Portis' heart isn't in it this time. The dispatching of villains is perfunctory, just a way to end the tale, and the villains don't engage the way the truly desperate desperadoes in "True Grit" did, and still do.

Still, the book has good things to offer. Among them, Jimmy Burns.

Portis, one of the fine comic writers of our time, can't resist making any character of his funny. It's the voice, the attitude, the world view. At one point in the book Burns' ex-girlfriend, who has heavy academic credentials, accuses him of being "afraid of smart women." He admits it, readily, then quotes two legendary (and often invoked) drinking buddies of his own on the subject: "Art and Mike said taking an intellectual woman into your home was like taking in a baby raccoon. They were both amusing for a while but soon became randomly vicious and learned how to open the refrigerator."

That's Jimmy Burns. He's hell-bent for old cootdom, but with an opinion about everything along the way.