Yamaha Trilogy: Hageman Seca 400

“We bought an SR400 for Sally,” Mike explains. “She’d learned to ride when she was younger, but was just returning to the sport. It’s a great bike, and the more time that we spent with it the more it seemed to me that you could work hard to make it cool, but in the end it wasn’t going to be any better than it already was, and it would be a shame to cut it up.”

An ardent fan of Yamahas of the late ’70s and early ’80s, Mike grew up during that era and has images of those machines almost permanently etched into his brain. Back then, he’d spend hours poring over the contemporary literature, and his first motorcycle was a Yamaha 750 Seca purchased in 1982.

“I was familiar with the 400 Seca, and thought instead of doing the SR400 the Seca might be a better bike to build,” Mike says. “Apart from the Atari/Tron styling of the original Seca 400, the bike has some cool elements.”

Mike became aware of those “cool elements” when he saw photographs of aSeca 400 without its bodywork. That’s when it dawned on him that the Seca, with its monoshock rear suspension and open frame, where the engine serves as a stressed member, was similar to how a Virago is constructed.

Greg has been dubbed “the Virago Whisperer” in the hobby thanks to his many custom Virago builds — and the subframe kits that he makes and sells that dramatically alter the appearance of these bikes — which prompted Mike to ask if he’d ever consider taking on a Seca 400.

“When Mike first started talking to me about it,” Greg says, “I thought it would be such a tiny bike with a small frame. But I told him, sure, I’d do it.” That affirmation set Mike in motion. He began searching for a donor Seca 400, finally finding one on Craigslist in Seattle, Washington. Not able to see it for himself, Mike hired a local motorcycle mechanic to go and inspect the machine. “He told me it must be one of the nicest examples out there,” he says.

The build

Mike bought it, shipping it to his home in Kansas City, Missouri. With only 5,000 miles on the odometer, the 1982 Seca really was in fantastic condition. Mike rode it a few times, but stored the bike waiting for Greg to call, and that happened early in 2017.

At the time, Greg was living and working in Tampa, Florida (he’s since relocated back home to Iowa). Mike loaded up the Seca and several parts, including about 10 gas tanks that he’d been collecting, thinking one might suit the build, and drove to Florida.

A half-day after unloading the bike and rolling it into Greg’s workshop, the Seca was apart. The pair began draping tanks over the stamped steel backbone of the frame, and when the circa-1969 Yamaha DS6 tank went on, they knew something good was in the making.

Bought for just $75 in an eBay auction, the tank was in great condition, and it offered an organic yet vintage look that was made all the better when the after-market made-in-China seat was propped up in position. According to Mike, Greg has many of these Chinese seats in his shop and uses them as styling bucks to see what works best. He only ends up using the pan, however, getting the seat professionally re-upholstered for the final product.

Stock, the Seca 400 came with fourspoke cast mag wheels. To replace those, Greg sourced a pair of wire wheel hubs. Introduced in 1977 on the heels of the XS360 of 1976, base XS400 models were equipped with spoked wheels and Greg used one of those for the rear. The front hub is from an XV700 Virago that featured dual brake discs. Greg machined away the right side disc carrier, leaving a single disc on the left. Both replacement hubs were laced to 18-inch Borrani flanged alloy rims using stainless steel spokes from Buchanan’s Spoke & Rim. Era-appropriate Dunlop TT100 tires were sourced from Japan, where Mike says they’re stock fitment on Kawasaki W650s and 800s.

Up front, the stock forks yielded to a beefier set of 41mm tubes and trees from a Yamaha XJ600, complete with aluminum Euro-style Krator 7/8-inch handlebars and modern controls from a Yamaha FZ-07. The newer forks allowed Greg to run a 320mm single front disc, 53mm larger than the stock 267mm rotor. At the rear, the Seca’s box-section swing-arm was kept, but the suspension was upgraded with a Hagon shock meant for a Yamaha RZ350LC.

After spending a couple of days with Greg, the Seca was basically mocked up. Mike returned home, leaving Greg to continue working out many of the often-challenging details that complete a motorcycle. Those included removing the rear subframe and welding up a new tubular support for the seat. This isn’t welded to the frame; rather, it’s bolted in place. To get the DS6 tank to fit over the wide backbone and to sit as far forward and as low as possible, Greg fabricated new top engine mounts. He also used a little heat and some well-placed hammer blows to re-form the tank’s tunnel to fit the Seca’s spine. Not a procedure for the faint of heart.

The mounts, Greg says, both on the tank and the frame, are similar to stock Yamaha fitments, but have been extensively reworked. Up front, a pair of ears on the tank slip over rubber cushions on frame stubs before a single bolt secures the tank at the back. The seat is similarly mounted, with a tab that slips into a receptor at the front, firmly secured at the rear with two 10mm nuts underneath. Continuing to work on the front end, Greg installed a Koso North America TNT-02 multi-function meter. The instrument includes an analog tachometer and digital speedometer and is supported in a custommade bracket. The 5-3/4-inch headlight is a high-quality LED unit with a glass lens made for the Harley-Davidson aftermarket. Taillights are tiny LEDs mounted into the rear legs of the swingarm to keep the back end as clean as possible, while the license plate is set vertically on the right side of the swingarm and washed in light by an LED. “Motorcycles always look better without signal lights and license plates,” Mike opines, adding, “but they have to be legal.”

Meanwhile, the double-overhead cam 399cc parallel twin engine with its 9.7:1 compression ratio and 69mm x 53.4mm bore and stroke was in good health. The crankshaft throws are 180 degrees apart, and there’s a counter-balancer that turns just in front of the crank to smooth out vibes.

According to an August 1982 Cycle World test, the engine is only 14.25 inches wide, narrower than most other Japanese models because it doesn’t have an alternator rotor mounted to the end of the crank; instead, the alternator is chain driven, mounted just behind the base of the cylinders.

In the transmission department, Yamaha endowed the Seca 400 with six gears, with power from the crank transferred through a straight-cut gear primary to a multi-plate clutch equipped with five friction and four steel plates. Of special note is the Seca 400’s YICS — Yamaha Induction Control System — cylinder head. The system, said Cycle World, is meant to aid “low-rpm economy and performance” by adding “a small passageway that intersects each intake port just ahead of the intake valve.” What it essentially does is create pressure in the opposite port, and the YICS “swirls and mixes the fuel charge in the cylinder, making it more homogenous for better burning.” The stock Seca 400 uses a pair of 34mm Mikuni constant velocity carburetors. Greg, however, opted for a pair of Mikuni VM34 round slide carbs with pod air filters.

Greg cut apart the Seca’s exhaust system, keeping only the header pipes, with a pair of 1.75-inch universal upswept mufflers from Niche Cycle Supply adapted to fit. Mike originally wanted to take Scotchbrite to the chrome exhaust parts to give them a brushed appearance, but the header tubes were not in perfect condition. Not a fan of exhaust pipe wrap, Mike and Greg finally settled on a matte black Cerakote ceramic finish.

The new rear sub-frame was powder coated gloss black to match the frame, as was the swingarm, which was originally silver. Wheel hubs, however, were coated satin black. The alloy fork sliders were polished, and Greg cleaned and detailed the engine by removing the side covers, also running them under the polishing mops. And the engine? With the side covers back on, Greg simply changed the oil and the spark plugs to return the engine to service.

When it came time to choose a paint color, Mike says Sall’s favorite hue is purple. During a visit with Greg in Tampa, both Mike and Sally suggested painting the Seca purple. Without missing a beat, Greg stared at them both and suggested orange. And that was okay, Mike says, because Sally’s second favorite color is orange. The tank was handed to Moe Roberts of Moe Colors in Tampa, and he sprayed it in a specially mixed House of Kolors candy tangerine. Reproduction Yamaha badges and a cream pinstripe finish off the job.

“It looks great in orange,” Mike tells me during a telephone interview, and then goes silent about the color while speaking to me. A few days later, Mike calls me back: “Sorry, I couldn’t say more,” he says. “Sally was in the room, and I couldn’t tell you I am having a second Yamaha DS6 tank painted purple for her June birthday. It’s a milestone birthday, and the bike is my present to her.”

Mike continues: “It was impossible to make the bike a secret, because I wanted her to have creative input — she wanted the number plates, for example — but I can swap tanks out on her birthday and surprise her. If she likes the purple better, we’ll run it that way. If not, I have a bunch of shelves in the garage with vintage Yamaha tanks displayed and it will rest there.”

With the custom Seca back in Mike and Sally’s hands, they put the machine on the scale. With a half tank of gas and full of oil, it weighs 357 pounds, about 40 to 45 pounds less than a stock Seca 400. Also, Mike reports the machine is nicely balanced at 50/50, nearly to the pound on the front tire versus the back.

The little twin-cylinder engine likes to rev, making a claimed 42 horsepower at 9,500rpm. Mike says peak torque is at 8,000rpm and the twin will happily rev to 10,000. Thanks to the YICS system and the pod air filters, the Seca makes a very distinct induction noise, and with the exhaust modifications the resulting note is neither overly polite, nor overly loud, producing a nice, mellow tone, Mike says.

A September 1982 Cycle test concluded the Seca was comparable to the sport-oriented 2-stroke Yamaha RD400. “It may not have the straight-line zip of an RD” Cycle said, “but the Seca is a more civilized and polished motorcycle, and in the right hands, it’s just as willing an accomplice as the RD when it comes to para-legal behavior on twisty roads.”

Regardless of how it’s ridden, this custom Seca will be a birthday present that Sally won’t soon forget, and in the garage it perfectly bookends the Hageman/ Martens trilogy of one-off Yamahas. MC