1981 Yamaha Seca XJ750RH: Even After 40 Years It Hasn’t Mellowed - UltimateMotorcycling.com
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The 1981 Yamaha XJ750RH Seca has an unusual, sculpted look and a raft of features most other 750s of its day just didn’t offer.
Looking back on it, I am amazed that I have owned this 1981 Yamaha XJ750RH Seca for 28 of its 40 years.What’s more, I owned an identical Seca, right down to the red metallic color for ten years before I got the one I still have and had both of them for three years!I have not owned any brand or model of motorcycle for a longer period than Yamaha’s 750 Seca, having acquired my first one 38 years ago! So, what is the attraction? Well, for one thing in 1983 the Seca was the largest displacement bike I had yet owned. Before that, a 1976 Honda CJ360T was the biggest bike I had owned. Needless to say, the difference in giddyup-go was very noticeable.
Fitted out with Slipstreamer Spitfire windshield, throw-over bags and small tail bag, the Seca makes a terrific day-trip or weekender touring bike.
The four-cylinder, four-stroke, double-overhead-cam, air-cooled mill that powers the bike put out a claimed 76 hp at 9,000 RPM—more than double the 34 hp at 9,000 RPM Honda claimed for my CJ360T. Skilled use of that power and the positive-shifting five-speed made for some pretty amazing performance in period road tests.According to Cycle magazine’s June 1981 road test, the standing-start quarter-mile was covered in 12.49 sec. with a terminal speed of 104.89 mph. Cycle World in its four-750 shootout covered in September 1981 did about as well in the quarter-mile: 12.52 sec/ 106. 25 mph. But in its June 1981 solo Seca road test, it did even better in the quarter-mile, turning a 12.34 sec. ET with a terminal speed of 106.63 mph. In that test, the Seca rolled up to an actual top speed of 119 mph at the half-mile mark.Those performance numbers are all for a Seca in box-stock trim. I acquired this one from a Yamaha mechanic who had added a Vance & Hines four-into-one collector and did the necessary carburetor jet work. Having had my first Seca with its original four-into-two exhaust and this one, but never having put either on a dyno, I can’t say for sure if either system had a performance advantage.I’ve been told the pipe and rejetting should add four to six rear-wheel horsepower, but I don’t have data on either of my Secas to back it up. One thing I can vouch for: the Vance & Hines pipe on my Seca delivers a sweet high-RPM howl that has had other riders asking me about the system.The 750 Seca has enough juice to keep things interesting and pull off a high-speed passing maneuver when the need arises. But, to be honest, in my kind of riding, which includes very limited interstate highway travel, all those numbers are really only fun to think about. Only rarely are the performance credentials of the old Seca put to the test, but when they are, the bike does not disappoint.So, if horsepower isn’t the factor that keeps the Seca in my shed, what is? It may be the factors that put the Seca out front of the 45 cubic inch field of competitors back in the day that keeps it interesting.Its swoopy, off-beat styling is one thing. It looks like most of the bike was designed using a French curve instead of a straight-edge. That design lends itself to a mildly stepped saddle leading to a cool rear cowling with an unladen seat height of only 30.8.”That is good news for me since my jeans have pretty low back pockets. So many of the bikes in the 750cc class I’ve tried out for fit have saddle heights that make manual from-the-saddle maneuvers difficult. Every one of the 750s in that four bike test I mentioned had higher seat heights than the Seca. The helical spokes in the cast alloy wheels are another interesting touch.
Crushed gravel roads in farm country hold no terror for the Seca. It’s no adventure bike, but it seems to handle pretty much all road surface conditions with stability and ease.
The Seca is just plain comfortable to ride. With midships pegs and slightly higher, pulled back handlebars that were added by its original owner and a very comfy, contoured saddle, the bike is easy to cruise on all day. With a Slipstreamer Spitfire windshield, semi-rigid throw-over saddlebags, and a small tail bag added, the bike is a terrific day-trip or weekend machine.Handling out on the road is superb and that’s one of the things that Yamaha put high on its design criteria when the Seca was on the drawing board. I keep the air-adjustable forks at 12-15 PSI and the rear twin shock damping presets at the second of four positions. I have found those settings comfy for routine riding but beefy enough to allow the Seca to make the most of its compact 56.9” wheelbase for quick, precise handling on twisty, technical roads without making the ride too harsh.How sweet handling is the old Seca? Purists may call it heresy, but among the 24 road bikes I’ve owned since 1974, including three Triumph Bonnevilles, I have to say, the Seca is more than a match for any of them. It turns with quickness and precision and stops with convincing power with the double-discs up front and the first-in-class anti-dive front suspension.The agility comes from its geometry: 28° of rake and 4.49” of trail and a chassis that, if anything is overdesigned to prevent frame flex that afflicted so many bikes in the seventies that had plenty of motor but not enough spine. The twin downtube, double-cradle mild steel frame is gusseted where it counts. Yamaha apparently wanted to avoid the faint praise bikes like Kawasaki’s earlier Mach IV 750 triple received that extolled its performance—but only in a straight line and quips like, “Norton developed the featherbed frame; Kawasaki had the deathbed frame.”This Seca had its original front disc brake pads and rear single leading shoe drum pads until 2018, when they finally needed replacement. Freshly refurbished, the brakes are as progressive and predictable as they are powerful. Period road tests complained of “vague” feeling, but I can’t say I’ve had any problem with that.It is in the front brakes that Yamaha broke new ground. In the seventies, the combined problems of rear-wheel lofting, reduction of ground clearance, and front suspension bottom-out under hard braking for race bikes in corners were addressed by various anti-dive front suspension systems. On the race track, the problem was solved, but it wasn’t until Yamaha introduced anti-dive front suspension on the 1981 Seca that such a system appeared on a street bike.
The Seca’s anti-dive front suspension works off the front disc brake and gives the front forks a unique appearance.
It gives the front end a rather exotic look. The standard brake line comes down from the concealed master cylinder to each single-piston caliper as you’d expect. But then things get weird. From the banjo bolt on the caliper, a second hydraulic line drops down to a gizmo on the bottom of the fork leg.Inside that gizmo, a spring-loaded poppet valve is activated when the right amount of brake line pressure is applied, as in hard braking. The poppet valve moves to restrict the flow of fork oil under compression damping, thereby momentarily stiffening up the forks by preventing the usual amount of fork travel. Thus, the forks won’t bottom out, the rear tire won’t loft, and the bike stays more level, so ground clearance isn’t reduced while cornering.Since the effect only happens when you need it to, there is no need to have overly harsh springs or damping settings in the forks allowing for a smoother ride. Slick.Unlike its contemporaries, the Seca had not one headlight, but two. In an over/under arrangement, it has a huge rectangular halogen high/low beam unit up top and directly beneath it has a smaller rectangular fog lamp. Last year, I finally had to replace the main headlamp bulb when the low beam burned out after all those years in service; the fog lamp gets only occasional use and as far as I know, has never been replaced. Edison would be proud.Instrumentation is where things really get cool and high-techy. All instruments, lights and read-outs are unified in one module. Very space-age.
The integrated instrument cluster is visually interesting and easy to read—and it works, even after 40 years.
There are an analog speedometer and tachometer, mechanical odometer, and trip meter as usual. Across the top, are turn signal indicators, neutral and high beam indicator lights, and a big, red warning light.The warning light works in concert with a menu down the middle of the panel for monitoring various functions or malfunctions as the case may be. Each indicating what the problem is with an LCD readout.The panel tells you when your side stand is down—and a kill switch on the side stand shuts off the engine if you put the transmission in gear with the side stand down. Below that are fluid level warnings for battery electrolyte, engine oil level (not pressure though), and brake fluid.Then there are warnings to tell the rider that the headlight or taillight are burned out, a low fuel warning, and at the bottom, an LCD fuel gauge. When anything is amiss, the affected function warning shows on the panel, and the red warning light flashes. At start-up, all the functions show in sequence like a pre-flight check on an airliner and then shut off if everything is in good order. If not, anything that is amiss stays on, and the red light flashes.At the very bottom of the panel is a “check” button that starts a system check on all those indicators on-demand after start-up and a “warning control” button that allows for the warning light at the top to remain in a steady glow state with one push of the button or to shut it off with two.Thanks to the comprehensive instrumentation for safety and operation, the Seca is a bike with a brain from way back! How cool is that?
The Yamaha Seca was my first shaft-drive motorcycle and it made me a real fan of the design. I have belt and chain-drive bikes as well, but when it comes to easy, clean, low-maintenance with year-in-year-out reliability, a shaftie like the Seca is hard to beat. 40 years in service without a repair says it all.
I know for sure that one thing that I love about this old bike is the fact that it has shaft final drive. No belt to keep clean, inspect and adjust and no chain to adjust, clean, and lube. Forty years on, that drive shaft is clean, quiet, and reliable.Low maintenance, too—just change the hypoid gear oil in the rear housing when you do your regular oil change and you’re all set. To be honest, since the gear oil has always been so clean when I would do it with every motor oil change, I now do it only on every other change and even at that it is clean-looking every time and virtually no residue comes out with drainage.After all these years, this Yamaha XJ750RH Seca is still a thrill that’s fun to ride, easy to own, and able to take me reliably most anywhere. And on the performance side of things, it hasn’t mellowed a bit.
Touring Michigan’s Upper Peninsula to the top of Mount Zion in Ironwood, MI, puts the Seca’s smooth power and easy ride to great use.For more on the off-beat Yamaha Seca, see:
1981 Yamaha XJ 750 RH Seca Tech Sheet:
1981 MSRP $3,199 USD2021 est. value $2,000 USD (Average, condition 3) per The Comprehensive Vintage Motorcycle Price Guide 2020-2021 EditionEngine Air-cooled, four-stroke, DOHC transverse four, 2 valves/cyl.Displacement 748 cc (45.64 in.3)Bore x stroke 65.0 mm x 56.4 mm (2.56” x 2.22”)Compression ratio 9.2: 1Carburetion Four 28 mm Hitachi constant velocity, Yamaha Induction Control System (YICS)Claimed BHP 76 @ 9,000 RPMPower to weight ratio 6.8 lb/hp.(fueled, unladen)Transmission 5 speed, constant mesh, wet clutch, shaft driveElectrics 12 v transistorized inductiveFrame Twin downtube, full cradleFront suspension Telescopic air-assisted coil spring, oil damped, anti-dive, 144mm travelRear suspension Twin shock absorber swing arm, 90mm travelFront brake Double disc hydraulic 298 mm (11.6”)Rear brake Single leading shoe drum 203 mm (7.9”)Front tire 3.25 H 19Rear tire 120/90 18Wheelbase 1,445 mm (56.9”)Seat height 782 mm (30.8”)Fuel capacity (Main/reserve) 14.9/4.1 L (3.9 /1.1 US gal.)Weight 521 lb. fueledCalculated top speed, 5th gear@9,500 RPM Redline 126 mph)The Link Lonk
March 12, 2021 at 08:47PM
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1981 Yamaha Seca XJ750RH: Even After 40 Years It Hasn’t Mellowed - UltimateMotorcycling.com
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