1982 Kawasaki GPz750 R1 chain/sprocket conversion from 630 to 530 pitch

Older bikes use 630 chain/sprocket pitch and it is getting harder to get. They are also normally non o-ring types which requires messy lubrication

To convert to updated 530 pitch the front sprocket, rear sprocket, and chain needs to be calculated.

Original 630 pitch:
Front: 13 teeth
Rear: 33 teeth
Ratio: 33/13 = 2.5

To convert to 530 system multiply by 6/5:
new Front: 13*6/5 = 15.6 ~ 16 teeth
new Rear: 33*6/5 = 39.6 ~ 40 teeth
new ratio: 40/16 = 2.5 ..... perfect

However I ride in the twisties often, and would like to have more acceleration instead of leisurely cruising speed. So I opted for larger rear sprocket (45 teeth)
desired new ratio: 45/16 = 2.8

Knowing that in the original ratio I cruise at 100kph at exactly 5000RPM  the new RPM can be calculated:
old rpm * (new_ratio / old_ratio)
5000 * (2.8 / 2.5) = 5600
So with 13 Front and 45 rear, I would cruise at 100kph at 5600RPM

For the chain, I just buy 120 link o-ring 530 pitch chain and cut accordingly. 530 chains are much cheaper at  $70 shipped from ebay.

After changing the chain, I felt that it is much quiter and smoother. And certainly easier to maintain in the long run with much less lubricant splatter. As predicted I now cruise 100kph at 5600RPM

photos:

16T front sprocket JTF513.16 available at Z1Enterprises but I bought it locally from PowerSport Kawasaki in Seaford













Rear Sprocket JTR488.45 from Z1Enterprises. This is the Emgo version which is much cheaper. If you would like to keep the stock gearing ration then the rear needs to be 40 Teeth ie. JTR488.40

Comparison between the sprockets. The front one is an exact match. The rear one is bigger as I had chosen it.

The front sprocket is tight, so no way to use a larger one like 17 or 18. It would hit the guard. 16 with 530 pitch is perfect.

Restoring full power to later GPZ900R models

Later GPZ900R power are reduced compared to 84/85 (A1-A2) due to emission requirements and perhaps as marketing strategy to sell their newer (but slower) bikes. The full power was 115hp and the reduced versions were 108hp.

I bought used carbs off 85 model (A2) from Ebay. From the outside it looks the same as my original ones, but it's got the following jets:

Main: 135
Pilot: 35
Needle: N27B

There are comprehensive information regarding the jettings between models here:

http://keihincvk40.blogspot.com.au/2013/12/the-keihin-carburettors-for-gpz900r.html

Tips: the throttle cable actuators are different. Later model use the push-pull wire, so if installing an A1/A2 carb you need to also buy the correct throttle cable. Or in my case I just moved the cable holders between the 2 carbs.

The next difference is airbox intake size. It's quite self-explanatory below:

And lastly, the original exhaust has different baffle length and diameter. Original exhausts are pretty much unobtainable so an approximate can be had by cutting the baffle like below.

The baffle can be taken out by removing the rivets and pulling it using some home-made tool such as long rod with a catch welded at the end. It took some hammering/persuasions as that narrow taper tightly pressed into an opening inside. But thankfully not welded.

After riding it I noticed much of the difference is at the top RPM, let's say 7500RPM and above. The engine feels to be spinning much more 'freely' and 'willingly' compared to before. I like it.