Project GPz

Besides the carbs are there any major differences between the 81 GPz engine and the 82 and later engines? I found a big bore kit for the 82+ GPz engine to punch it out to 615 cc and was wondering if it would work in my 81s engine. If so..i see a full tear down in my future lol...

The '81-'83 have the same 10:1 compression ratio, according to the White Kawasaki Factory Manual. It also states the '81(D1) and '82(H1)-'83(H2) have the same cams and timing. Neilage and Loudhvx both have '81's and could tell you if there's anything different in the engine department. If you buy the 615 kit, send out your cylinders to have them bored with the kit. I bought my kit from APE, and they gave a discount if you bought the kit from them, as opposed to sending them a kit with your cylinders. They machined the cylinders, and rebuilt my cylinder head too.

If your engine has some miles on it, and you're planning on keeping the bike, before you install the 615 kit, rebuild the bottom end.

You'll have to rejet those carbs. I have the Stage 3 K&N Kit with 134 mains in there now, and plan on upping the mains if necessary. See what your options are for main jets on your stock carbs, and if there are replacements. There is a Stage 3 Kit for your carbs floating around out there somewhere. Below is what would come in the kit:


Good luck.

Where would one purchase a Puig Cockpit flyscreen like that one?

OutlawGPz wrote:

Besides the carbs are there any major differences between the 81 GPz engine and the 82 and later engines? I found a big bore kit for the 82+ GPz engine to punch it out to 615 cc and was wondering if it would work in my 81s engine. If so..i see a full tear down in my future lol...

The head and cylinder block are different castings.
The head gasket, however, is the same.
Same comp ratio.
Same bore.
Same stroke.
Pistons and wristpins are the same.
Crank and secondary-shaft parts are the same.
Con rods and bearings are the same. (There appears to be a typo on the '82 fiche parts list for a bearing.)
Transmission parts are the same.
The head has larger intake ports on the 82/83 for the larger carbs. Carb center spacing is the same.
The valves and valve parts are the same.
The cams are the same but 81 has a tach drive cut into the exhaust cam. (Intake and exhaust have same profiles.)
82/83 has no mechanical tach drive.
Valve cover gasket is different.
Cam chain tensioner is different.

As to why a 615 kit for an 82/83 wouldn't work on an 81... this is a wild guess... perhaps the liners on the 81 cylinders are thinner and can't be bored out as much?

Post edited by: loudhvx, at: 2007/10/22 03:01

the catalogue didnt have a listing for the 81 but it didnt say anything about not using the kit for the 82 in the 81 engine...im thinking im gonna have to do some more research on the matter..

Bringing this old thread back to life since i had sold the GPz to my roomate and it sounds like im getting it back since he wanted a larger bike. I had bought his Interceptor from him as well but we recently made another deal and i got my old CB750 engine back (it was to be used in the drag bike but that didnt pan out.) Anyways...Since now that the bike i had in the shop at the time i had this before is out of the shop and puttin on miles again i can focus on this bike. I still need to get ahold of a wiring harness from a GPz 550 unless a standard KZ550 harness will work. The wiring harness is this things biggest issue followed by the forks and shocks...i get those 3 points taken care of this bike will be back on the street.

FREE MANUAL-> www.metrovationinc.com/christemple/KZ550.pdf