Fans of “Grindhouse,” the epic-sized Quentin Tarantino-Robert Rodriguez homage to exploitation movies of the seventies, will rejoice at the appearance of this “Mexploitation” flick, inspired by the ersatz trailer that Rodriguez made as one of the transitional pieces in the 2007 picture. And for a while the joke is pretty amusing. Unfortunately, like “Grindhouse” itself, it doesn’t know when enough’s enough.

Danny Trejo, the veteran tough guy whose weathered face and unruly mane you’ll probably recognize even if the name’s not familiar, plays the hulking hero, an incorruptible Mexican federale whose wife and daughter are killed by drug lord Torrez (Steven Seagal). Left for dead by the nefarious kingpin, he makes his way across the border to Austin, where he’s a simple day laborer, though one still adept with his weapon of choice, which gives him his nickname.

But things are hardly idyllic in Texas. State Senator John McLaughlin (Robert De Niro) is using anti-immigrant fever to campaign for re-election, and he and his unscrupulous manager Booth (Jeff Fahey) are in league with ruthless vigilante Von Jackson (Don Johnson) and his army of redneck gunmen. At the other end of the spectrum is Luz (Michelle Rodriguez), leader of The Network, a ragtag group that helps illegals cross the border and stay in the US. And in the middle is Sartana (Jessica Alba), an immigration agent who’s conflicted about the policies she’s supposed to enforce.

The plot kicks in when Booth decides to improve McLaughlin’s electoral chances by staging an assassination attempt on him, using Machete as the patsy who’ll be blamed. Naturally Machete escapes, and allies with Sartana and Luz to uncover the truth. He also involves his brother, a wily priest (Cheech Marin). But when his own men don’t prove up to the task of dealing with Machete, Booth brings in heavy-duty help in the form of master hit-man Osiris Ampanpour (makeup specialist Tom Savini). And as you knew he would, Seagal turns up again as the ultimate villain in the plot.

This is all shlock nonsense, of course, cobbled together from bits and pieces of every sort of exploitation flick you can imagine. But for an hour or so it’s over-the-top fun, with the totally gratuitous soft-core interludes and heavy gore moments adding to the feel of low-brow goofiness; even the shots in which stunt men replace the bulky Trejo in action sequences are sophomorically enjoyable. And the cast throw themselves into the act. De Niro is certainly no comic, but he tries his best at a parody of a right-wing demagogue (and comes to an appropriately, if heavy-handedly, ironic end), while Fahey plays it straighter. Alba and Rodriguez do their action heroine shtick with energy and look luscious. Johnson (whom the credits “introduce”) is all lip-smacking malevolence. Marin does his thing. And to add to the mix, Lindsay Lohan, of all people, shows up, does a nude scene and then dons a nun’s cassock and a machine gun. She’s terrible, but maybe she was on loan from rehab. Even worse is the bulbous Seagal, whose acting is worse than his accent, and whose culminating face-off with Trejo has to be so carefully staged—both men obviously past their prime—that it must have taken days to complete.

For about an hour, however, the silliness works. Unfortunately, the last 45 minutes go south, as it were. You can sense Rodriguez straining harder and harder for effect, ending up with a big final shoot-out that’s chaotic, with the humorous bits generating far fewer laughs than intended. By that time the political message has reached astronomical proportions too, and while that might appeal to many viewers, sharper handling of it would have really helped.

So if you’re happy with a decent hour’s worth of movie, this may work for you. But it might have been better had Rodriguez, working as editor with Rebecca Rodriguez, used the title implement to chop some off the latter half. And as for the two sequels promised at the end, again in exploitation-flick style, they should probably pass.