SANTA CLARA — Offensive coordinator Greg Roman, in discussing how he has simplified the 49ers offense, kept it uncomplicated himself.

“If it works, it’s good,” he explained Thursday. “If it doesn’t, it’s not.”

Right now, it’s clearly not.

Roman’s offense is a sputtering jalopy as the 49ers (7-5) gear up for the Raiders (1-11) on Sunday. The 49ers have a fleet-footed quarterback who barely runs, a record-setting tight end who has vanished in plain sight and a Hall-of-Fame caliber rusher who can’t find his rhythm.

The 49ers have scored fewer than 20 points in five of the past six games. Their most recent outing, a 19-3 loss to the Seattle Seahawks, was so aesthetically displeasing that it prompted owner Jed York to tweet an apology and the general manager’s daughter to take aim at the man calling the plays: “Greg Roman can take a hike. The 49ers don’t want you no more.”

Coach Jim Harbaugh countered quickly with a vote of confidence for Roman — “I have unwavering support for all our coaches and our players” — but the coordinator’s approval rating among the fan base is at an all-time low.

So what’s wrong with the offense?

That’s where it gets complicated.

Colin Kaepernick’s stagnation is the biggest bugaboo, and experts are split over how much of that falls on Roman’s play-calling and how much falls on the quarterback himself.

Kaepernick’s passer rating was 98.3 in his first full season, 91.6 in his second and 87.8 this year. His eight interceptions match his full-season total from a year ago. And there’s no sign of the supernova runner who burst upon the scene in 2012 — Kaepernick has zero rushing touchdowns this season and no run longer than 23 yards.

Some of that stems from Roman’s effort to simplify the offense. But Rich Gannon, the former MVP, said it really starts with Kaepernick.

“To me, he just doesn’t look comfortable in the offense. … People say, ‘Fire Greg Roman! What are they doing? It’s vanilla,’ ” the former Raiders star told Sirius XM Radio. “Why do you think they’re scaling it back? That’s what the fans out there need to understand.

“What, do you think the coordinator got dumb overnight? You think Jim Harbaugh doesn’t know what he’s doing? The quarterback’s not making the right decisions. The quarterback isn’t making the right checks. So what are we going to do? We’re going to make it more simplistic. We’re going to have a little bit less volume in the offense.”

Greg Cosell, a senior producer at NFL Films, cited a specific example against the St. Louis Rams earlier this season. He said that on third-and-short, the Rams defense played a Cover-Zero — meaning no safety in the middle of the field. In his film review, he saw Roman had a play call to beat that defense with a post route for (Michael) Crabtree to run through a “wide-open middle.”

“(Kaepernick) needs to know right away that that’s where the ball should be thrown,” Cosell told KNBR radio. “But he was totally focused on (Anquan) Boldin, who was double-covered. No recognition. And Kaepernick just dropped his eyes and ran into a sack. Plays like that are what concern you over time, because that’s pre-snap recognition.”

But others argue that the 49ers’ widespread offensive woes start in the coaching booth, and that Kaepernick remains an electrifying threat bottled up in an unimaginative offense.

Consider that in his previous meeting against the Seahawks, the quarterback ran for 130 yards in the NFC Championship game.

But against Seattle last Thursday, Kaepernick didn’t take off on a single designed run.

Former 49ers lineman Derrick Deese, speaking with 95.7 The Game, noted that Steve Young, his Hall of Fame teammate, had the skills of a pocket passer but got really dangerous when he rolled out and gave the offense another dimension.

“Colin is able to do that stuff,” Deese said. “His first year, it was like they were calling plays for him to do that. Now it’s like they’re holding him back. They need to tell him, ‘Hey, look, if you don’t see it, just go.’ And he needs to go.”

Roman’s offenses have never been explosive: The 49ers ranked 26th overall in his first year, then 11th in 2012, 24th in 2013 and 22nd this year.

The 49ers have topped 30 points in a game only once this season, in a 31-17 victory over the Rams, and that score required an interception return for a touchdown by Dontae Johnson.

Fullback Bruce Miller acknowledged earlier this week that the 49ers are keeping things simple, including scrapping much of the pre-snap motions and shifts, because opponents have caught on.

“I think that’s gone, creating the confusion,” Miller said. “I don’t think we’re getting the reaction from defenses. I think that has caused some error on our part.”

Roman, like Harbaugh and Kaepernick, plays things close to the vest with the media. But he indicated Thursday that simplifying the offense had nothing to do with Kaepernick. Instead, he acknowledged that the 49ers might be hamstrung by a beat-up offensive line.

The projected starting unit of Joe Staley, Mike Iupati, Daniel Kilgore, Alex Boone and Anthony Davis has been together just once all season — a 26-21 victory over the Philadelphia Eagles in Week 4.

The makeshift O-line would also help explain a down year for Frank Gore, who is averaging only 59.3 rushing yards per game.

Meanwhile, tight end Vernon Davis, who scored 13 touchdowns last year, has just two this season, both in Week 1.

“We’ve had guys in and out (of the lineup) and all that, but I’m not going to stand up here and make excuses,” Roman said. “We’ve got the players to get it done, I know that. I know we’ve got the coaches to get it done. We’ve got a rich tradition of getting it done.

“And we need to dial in. And whoever’s out there, we’ve just got to simply get it done. And that really starts with me.”

Contact Daniel Brown at dbrown@mercurynews.com.