The GPz1100 Collection

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I have managed to accumulate a couple of Kawasaki GPz1100’s over the last couple of years. All are in running order and all will get a “make over” in due course.  The collection consists of (in date order), a 1981 GPz1100B1,  1982 GPz1100B2 and a 1983 GPz1100A1 (also known as a ZX1100A1). To help others I wrote an article on the GPz1100 series on Wikipedia as a reference between the different models.

1981 GPz1100B1

In July 2008 I purchased a GPz1100B1 for $2000. it had been sprayed black with gold pin stripping, it rode OK but could be substantially better and it needed some suspension work done, the rest of the history is unknown. Then in June 2009 I had to sell it after my marriage ended, but recently I managed to obtained it back! As the previous owner ended up doing nothing with it and it was left to gather dust!

The B1 is currently partly stripped in the garage and awaiting a full strip and rebuild so I have scheduled January 2012 as the start date to organize space, storage for the bits and to begin the complete dis-assembly and rebuild once I complete the GPz1100B2. At this stage I will keep the DFI system as its still fitted and working OK but it will get a Megasquirt installed and tweaked to suit the 1100 engine characteristics.

1982 GPz1100B2

I purchase my GPz1100B2 in February 2008 for $2000. It was up for auction on eBay but I missed getting to a computer in time and the auction ended! lucky for me there were no bids as the model was not popular despite it being in my opinion the most reliable Zed ever build prior to the GPz900R. I contacted the seller and he agreed to let me have it, subject to inspection, for the offer price. The owner had it for 16 years but had only ridden it a few times in the last couple of years and due to a lack of maintenance the brakes were seized and the clutch often locked up when the lever was pulled in. The disks were worn but the motor starts first go and purrs as it had just been rebuilt with a 1175 kit and a bit of extra work. I have not confirmed the large pistons but in the future when the engine needs a strip I will be able to measure everything and see if this is the case.

Other points to note are that the calipers were full of crap and needed a good clean up to remove the build up of grime that often occurs around the seal.

The work done to date has been:

March 2008

  • Installed new disks and stripped the brake calipers.
  • Installed new battery and pulled clutch lever actuator apart to clean out the old grease.
  • Checked the wiring, lights, horn, instruments and blinkers.


  • Roadworthy obtained.
  • Have obtained new SS304 Banjo bolts so I will strip calipers off again and replace old bolts then bleed brakes again.

Notes: Calipers are crap, so I will eventually fit GPz900R calipers as they work MUCH better and are a bolt on with minor work.

June – Intend to register bike when rain stops!

July – Registered… but… After sitting for six years the fork seals have proven to be shot, so with me now riding it everyday the leaks started big time. A new set of seals was obtained from England and fitted one Saturday morning in 2 hours 20 minutes. The 2 hours was to do the first one, the 20 minutes was the second fork leg, once I worked out how it was all assembled (very easy to do).


A few things to work on prior to a trip to Phillip Island for the MotoGP.

The Alternator has blown or was already blown, the battery has been slowly going flat. On disassembly of the unit, a big black burnt section was noted in the windings in one area (pictures to follow shortly). Replacement unit will be obtained this week.

The front tyre is at a point where I have now replaced it with a Metzler Lasertech 100/90V19. Rear should be good for 5000klm and is currently a Bridgestone, I will replace it with same when I get back as the Bridgestone is not a bad rear tyre.

Gear Ratios
A run out to Kingaroy for a camping trip on the weekend at the “Tinny Rally” indicated that the sprocket gearing is wrong, at 100klm/hr the engine was doing 4500 rpm, it should be doing 3500 or thereabout as it is an 1175cc engine with heaps of grunt. On disassembly of the rear end, I discovered the sprockets are not standard ratios. The front is a 14 tooth but it should be a 15 tooth and the rear is a 41 tooth instead of the standard 40 tooth. As a result of this the bike revs higher for less top speed. I need the bike to get to the MotoGP in October so I need it to be cruising down the highway, not revving its guts out! new sprockets on order! If I cannot get a 15 tooth front then I can go down to a 37 tooth rear to get a better top speed.

Fork Seals
The fork seals have proven to be OK after I changed them out the other weekend, this means the fork sliders appear to be good.

I dropped the speedo over to Otto Instruments for a service, it is making a whirring noise that is typical of a worn bearing and should get a re-calibration at the same time. Update 25th August 2008 – picked up speedo today, its was reading 102 at 100 and 200 at 190 klm/hr. The defective bearing has been replaced and all is well, will refit tonight.

Sump Oil Leak
The only issue left is the sump leak. I need to do a filter and oil change, so I will drop the sump also and check the sludge in the bottom to get a feel for the state of the motor. On return from Philip Island I will need to do shims and another oil change.

Brake Calipers
Despite my initial strip and clean of the calipers when I bought the bike to get it to roll, I have discovered there is brake fluid weeping from the calipers, so I will need to replace the seals in October if I don’t do it sooner. Update – Three (3) new kits ordered from Z1enterprises.

Bike back and running by the weekend. Just need to fit the speedo and bikini fairing.

No other faults at this stage!



4 thoughts on “The GPz1100 Collection”

  1. very interested if you managed to fit new calipers to the b1?
    l have a b1 and now the old calipers are fairly worn out.Do you know if the late 900r A twin pot tokico calipers will fit?
    many thanks

    • Sorry for the delay Peter, If the centres of the mounting bolts are the same then the should fit but you then need to see if they align evenly over the disks. I suspect the disk on your source bike will sit tighter to the forks so you may need to include spacers between the caliper mount and the fork leg. Either way its going to take some experimentation.

      The A1 calipers fit the GPz1100B2 but need spacers and sit slightly up off the disk by a few mm and work brilliantly. As the B1 has slightly smaller disks I suspect they also work but juts sit off the disk a bit more. You could always make a new caliper mounting bracket or try to re-drill the original one. Maybe a GPz750 caliper bracket is a better fit?

  2. vince baker said:

    Have you found a replacement for the throttle valve switch (throttle position sensor)
    on the B1.
    This part is no longer available. Is there a megasquirt system to replace the B1 system

    • Hi,

      I doubt highly there is a direct plugin compatible TPS, however there are numerous TPS modules that could be adapted to fit. If you visit the various megasquirt pages and have a look I am pretty sure many will list TPS’s available that could be made to fit.

      As for a direct replacement, no, you will need to do a fair bit of work to fit it and get the tuning right. The B1 and B2 have different injection systems and will require some work to convert over.

      It will make a great project so let me know how you go.

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