My 91 ZXR750R

My 91 ZXR750R

Introduction:
As you might have gathered, this is the limited edition K1 race model that Kawasaki brought out in ’91 to comply with Superbike homologation rules. Complete with Flatslides, Close Ratio gearbox, Higher spec suspension…….and of course……attitude!

Modifications so far:

Engine and Exhaust

    • Muzzy stainless steel header downpipes
    • Micron Titanium Oval Race can
    • Aftermarket bodywork
    • Racekit Magnesium Cylinder Head cover
    • Iridium spark plugs
    • Removed clean air system
    • 4 Degree Ignition advancer
    • Slipper clutch tuned to “intermediate” settings (4×2.0mm and 3×2.3mm plates) as per Racekit manual spec
    • Racekit “medium” clutch springs

Airbox and Carbs

    • Airtech Ram-air race airbox (modified and using a home made filter)
    • Coils relocated behind the new airbox (used ZX7R-P coils and leads)
    • Racekit floatbowls with one accelerator pump
    • FCRs re-jetted to suit the new airbox
    • Removed “choke” enrichner actuating bracket from FCRs
    • Removed fuel enrichner solenoid
    • Removed fuel tap (using shut-off fuel couplers)
    • Only using reserve fuel feed from the tank

Frame

    • GSG Moko frame protectors
    • Racing engine cover (right hand side)
    • Racekit CrankCase protectors (left and right hand side)
    • Swingarm crash bobbins
    • Forks crash bobbins
    • Robby Moto rearsets

Brakes

    • Brembo 19X20 Master Cylinder
    • Goodridge steel braided brake hoses
    • 6 pot Gold Tokiko brake calipers (from a GSXR1000K1/2)
    • EBC HH brake pads
    • Viper Stealth Wave brake discs
    • Bleed banjo bolt fitted to the front brake master cylinder
    • Gold Nissin rear caliper (from a GSXR1000) with Nissin pads
    • I had the stock caliper carrier bracket modified by Pretech Engineering so as to do away with the torque arm
    • Removed rear caliper torque arm (see above)

Suspension

    • “P” model shock linkage rocker with Racekit tie rods
    • Ohlins shock tailored to work with the P model linkage above
    • WP Steering Damper

Chain

    • 520 Tsubaki chain with Renthal alluminium rear sprocket and Renthal ultralite steel front
    • Fitted “Pull” type chain adjusters to the swingarm instead of the stock adjusters

Other

  • Digital speedometer (removed stock speedo drive at the front wheel)
  • Alluminium fron wheel spacers
  • Race Clocks
  • Removed thermostat + housing for better cooling (not recommended in winter though)
  • Smaller coolant bottle strapped behind the radiator
  • Shut-Off fuel couplers to facilitate tank removal
  • Modified the RH handlebar switchgear to allow fitment of Quick Action throttle housing with choice of throttle (also makes removal of carbs a lot easier)
  • Carbon fibre Hugger and chain guard

More Info:
Follow the link to see the Full Specifications.
To compare with other ZXRs follow the links on the History page.


Riding Impressions:
I remember my first impressions when I got on the ZXR750R. I was going on a short test ride prior to potentially buying the bike. The handling surprised me as I did not expect it to be so good. The previous owner had made a bit of a mess with settings, despite that the bike still handled impressively well. Next was the power delivery. I was not familiar with Flatslide carburettors or Close Ratio gearboxes and I nearly stalled the first time I tried to do a fast getaway, but once you wind the engine up above 5-6000rpm the way the power comes in is simply mad and addictive. The brakes have lots of power an feel and the bike is very composed even when braking really hard. I never fancied trailing the brakes into a corner, yet the amount of feedback you get is such that you find yourself doing it just because you feel you can.

Having said that the shock linkage is too progressive making the rear suspension too stiff. It is OK for the track, but on a bumpy road it just forces you to back off. Even on the track the shock linkage is the weakest link (after the rider that is). Luckily this can be cheaply and easily fixed (see further down the page).

Of course the bike can be improved (see mods further down the page), but it is a surprisingly good package already.
The ZXR750R is a pretty uncompromising bike to ride. It demands that you learn it well and adapt your stile to make the most of it. But it rewards you by forcing you to hone your skills. Everything you do on this bike matters as it has a direct effect on the resulting performance. The bike’s sensitivity to rider input and the level of feedback allow you to really work on your technique and see the results.
Then there are the looks. Mean, sleek and aggressive. The styling hasn’t dated and it still looks drop dead gorgeous.
Since I bought it I have come to appreciate another aspect of it, the “Rarity” factor. You will hardly ever see another one around and, I must admit, that feels pretty special.

A few years back In an article comparing a ZXR750RK with a bored and tuned ZXR750J Performance Bikes magazine summed up this bike beautifully:

“The banzai approach of the K has a deliciously irresponsible flavour which is as impossible to rationalise as it is to resist. Wild strawberries are invariably harder to find than the domestic variety but they always taste nicer”
 

Top modifications to make:

  • The best and most cost effective performance modification that you can do to a K model (or a J one and probably an M for that matter) is a shock linkage from a later L, P or N model. I bought a P model linkage for £25 (GBP) from a breaker and fitted it using the original K1 shock. The difference is amazing. The new linkage allows the shock to work as it always should have done. See K1 suspension Mods for more info.
  • Upgrade your calipers. Look here for all the info on the 6 pots brake calipers upgrade!!!.
  • Tune your Slipper Clutch A little known fact about ZXRs and ZX7Rs is that all models from 1989 to 2003 are equipped with Slipper Clutches. The reason most people don’t know is that Kawasaki set them with minimal slip at the factory. Here are the Racekit tips that allow you to activate them: Tuning the Slipper Clutch.
  • Coolant Bottle. If you own a K model you know how maddeningly difficult it is to remove the seat unit (one piece item) with the coolant bottle in the way. for this reason I thoroughly recommend ditching the stock coolant bottle and replacing it with an R1 item. The latter fits beautifully in front of the radiator on the right hand side and can be secured to the rad with cable ties.
  • Tyres:
    Dunlop D207RR (Race Replica): These tyres are excellent. Good grip, turn in speed and feedback. Any rear wheel slides whilst on the power and well leant over are surprisingly predictable and controllable (I am no GP God). They also seem to last very well despite the abuse.

    Pirelli Dragon Supercorsa: I have now tried them on track and they are excellent. They need a little more warming up than the D207RR, but once up to temperature they feel even more surefooted in corners. They wear quite well too (considered how sticky they are). Avoid the rain though as, given the minimal tread pattern, they are NOT wet weather tyres.

    Suspension:
    Setup1:

    Forks Preload – rings showing Ride Height – mm from top yoke Rebound – clicks from fully in Compression – clicks from fully in Tyre pressure (PSI)
    Max – Min
    8
    n/a
    13
    8
    n/a
    Standard
    8
    3.11
    7
    4
    33
    My Setup 28/08/2001
    6
    10
    4
    2
    31
    Shock Preload – mm of thread showing Rebound – Adjuster settings Compression – clicks from fully in Ride Height – Spacer size in mm Tyre pressure (PSI)
    Max – Min
    ?
    4
    25
    Standard spacer (10mm)
    n/a
    Standard
    ?
    2
    7
    Standard spacer (10mm)
    36
    My Setup 28/08/2001
    25
    3
    14
    Standard spacer (10mm)
    35

    Setup2 (with P model Suspension Linkage and tie rods):
    Forks as per Setup1

    The weather as just turned much cooler and wetter and this has hampered my testing somewhat, but I have managed a few decent runs last weekend. Although the compression is now set at 16 when the weather is warmer 15 is the better option.

    Shock Preload – mm of thread showing Rebound – Adjuster settings Compression – clicks from fully in Ride Height – Spacer size in mm Tyre pressure (PSI)
    My Setup 21/10/2002
    36
    3
    16
    Standard spacer (10mm)
    34

    Setup3 :
    I am now using an Ohlins shock at the rear, a P model rocker arm and racekit tie rods (and more mods are to come soon). Because of this I am not going to post my latest settings as they would only be of use to people with identical setup

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