Alistair Maclean's Web Site
Yellow Peril

Where's the beef?

Ready to go for a ride, the yellow peril from Yamaha

The Yamaha Seca II that I own is not the worlds most powerful machine. In fact it lacks a great deal in the engine department. However, that said, the use of a jetting kit and some handy repair work by my friendly dealer has given the bike a new lease on life. Noticably buzzy, the bike becomes galssy smooth at almost exactly 4,100 rpm. Below these revs, the machine is quite a vibrator, above say 6,000 rpm and the vibes return. But in that sweet spot, this is a very smooth runner.

Power wise, this bike makes a good bit more horsepower than the old KZ550, but it is just not reachable in the same way. While the Kawasaki would rev in 6th down to just under 2000rpm and then pull away, 2 up, the Yamaha has to be making more revs. Somewhere over 7000rpm, the thing is making decent power, but it's not a really rev happy motor, so it takes a good while to get there. All in all, the old KZ I contend made better and more useable power.


Originally the bike came with incredibly lean jetting. It required 10 minutes of warm up before the beast could be ridden, even then it would stutter and stall. I called Chaperal and ordered a Stage 1 jetting kit. The kit was relatively easy to install, though I was less than thrilled to be taking a drill to the slides.

The bike had been running quite roughly before I messed with it, starting to run on something less than a full 4 cylinders above half throttle. It was no better after I did the jetting and cab sync'ing. This is where my good friends at Rizzons stepped in; stripping and rebuilding the carbs. The effect was stunning. The mechanic told me that one problem had been that the rubber seals under the main jets had become crushed. I have to say that this could have been my fault, but don't recall ever taking the main jets out (I don't think is was required as part of the re-jetting).

Since fitting the jetting kit a whole series of issues seem to have cleared up:

  • Warm up is much shorter
  • It runs cleanly even after a short warm up
  • There is much more snap to the throttle action
  • It doesn't seem to overheat in traffic
  • It doesn't hunt on a constant throttle setting
Things are not entirely fixed. I think that the jetting may be a bit rich in some throttle positions, as evidenced by a slight fluffiness when opening the throttle quickly, and an unwillingness to rev out and haul more than 100mph, this may be something an aftermarket exhaust pipe would clear up. Funny how we need to fix more and more things on our bikes!

Handling; the Seca II handles very nicely. Its wide bars allow a gentle pull on the bars to initiate fairly brutal turn-ins. The front end handles these well, even the forks don't seem to mind the abuse. The rear is good, but not as good as the front. The rear shock is a bit squishy, even on the stiffest pre-load setting. It's not bad out back, its just that you get what you pays for, and as this was a fairly cheap bike, even new, the components it was fitted with showed less than optimal performance. I suppose an aftermarket shock would help measurably. The rear shock is pressed by my 250lbs of lard, exhibiting noticeable wallow when thrown around, or in hitting bumps mid-corner.

In summary the Yamaha Seca II...

  • Is a 4 cylinder motorcycle
  • Displaces 597cc
  • Has a single disc brake up front and disk at the rear
  • An engine that requires jetting
  • Handles well
  • Has a large, partially comfortable seat
  • Has a 3.4 gallon (Imperial) fuel tank
  • Gets between 35 and 55 mpg
  • Has done 135mph on the clock (usual inaccuracies a proviso)
  • Is a nice bike to go slowly on
  • Could be a good learner or intermediates bike


The Seca II comes without a centerstand, but Yamaha does (or did) list a centerstand as an aftermarket part. I got one and fitted it. It's amazing how often it gets used.

The rear tyre was junk in under 4000 miles, so I replaced the front and rear with Michelin Macadam 50's in the standard sizes. These tyres seem to be fine, given the bikes inability to make high horsepower numbers.

As an aside, the Seca II is also known as the Diversion in Europe. There are differences between the models, but generally they are same. One variation which has a friend and I scratching our heads over is what looks to be a chain rensioning system on the Seca which is not on the Diversion. It may just be different model years, or it may not be a cam chain tensioner. The diversion had some different colour and graphic options but is generally the same FJ600 inspired ride.

For as long as I have had this bike, it has a fairly low mileage, but that has not stopped some parts from giving up life. The most recent failures have been the coils and the little plastic screws that hold the windshield on. The coil failure presented itself initially as a hesitation, but as it got worse, the engine began to run on 2 cylinders intermittently. A number of years ago, I bought a set of Accel coils for this machine through Chapperal. I fitted these in about 2 hours and now the motor runs quite smoothly once more. However, in taking the fairing off to get at the space the coils live in, the small plastic screws that hold the screen on lost their heads. The heads going a little white through oxidation, must just have seen one too many turns. Three of them failed. At once. So now I have to order parts for an 11 year old bike... At least they manufactured the model till just a few years ago.

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