[Peterex]

Hy everyone!

I write this article to share with all of my tuning, and developments of my old 1st gen gpz 500 s.
The background live of my bike: 1993 1st gen gpz 500 s, with a 20 kw choke. The last owner had the tipical selfkill gpz issue. The flywheel magnets fly away and kill the bikes engine. So when i bought it it have an gpz cyilnder and new pistons, and er-5 cylinderhead and camshafts. So now the bike now somewhere 35 kw. Flywheel is came from mitsubishi and its have 1 round magnet.
Modifications:
Carb: GPZ 500 s 1st gen needles with 130 main jets. Better low end torque and throttle reaction. No more hp or higher top speed
Airbox: I make 1 more 1 inch hole in the airbox, like the FOG mod, but this not the fog mod, because i not buy the K&N air filter. i buy a new original. Better throttle reaction every RPM.
Exhaust: The stock has the wisthleing issue. Very irritating. Change it. I like to order a used er-5 2-1 exhaust to fit the cylinder head and the camshaft, and they send me something else. It was a 1986 gpz 900 right side 2-1 exhaust manifold without the muffler. Hmm, what ever try it. i install it. Its fit, with the original brace and i buy for it, a 2004 kawasaki z750 muffler. With these two modification i had an other bike. More torque, and a different sound. This exhaust havent got that piece of tube witch connect the two pipes before the muffler. Its sound deaper, and firing back when its hot and i use engine brake.
Chain sprocket: After these modification i have a very good bike, but i dont like high rpm, so i buy a 17 teeth front sprocket with stock rear and a new chain. Difference: 5000 rpm--> 100 km/h 9000 rpm 180 km/h GPS, this is the top speed, but its in every time. Less fuel its need.
Rear: The drum brake was terrible. and the swingarm was heavy. The 1986 gpx 600 swingarm is fit. So change it. swingarm, wheel (very simila to the original), sock absorber, disc brake. Much better in the corners alone or with passenger. BUT--> now the front is sh.t.
Front: Progressive springs, 15 w fork oil. and a fork brace. Now equal good the rear and the front suspension. Much sharper the hole bike, feels lighter and younger. Better cornering in high and low speed to.

I have an other bike. A Yamaha SZR 660 wich is a race bike. When i bought it I realized that the GPZ is not a good bike, but i love it, so i don't like to sell it. So i developed. Now the difference between the to bike's is not a grand cayon just a ditch. Its still have difference, because i tuned the GPZ for myself, and the SZR it s a factory racing bike, but with better technice i can catch the SZR and my wife in the mountin roads.

This was how i tuned my GPZ to be a good bike. Now its much better than i bought it. And i think i never sell it. If its ever breaks down (I dont think) I'll buy KLE 500 and use its part, and sell others to live in other old and good EX 500 bikes.

Thank for reading.

Pete

 

[yorkie]

hi welcome to the forum and your first post. I noticed the Hungarian flag on your avatar so English is not your first language well done making such a longish post readable and with only minimal errors. thank you.

that is quite an insight into how non mainstream mods can be done on these bikes lifting the lid so to speak on how to and not how to do things. in the end you have a bike your happy with and want to keep it that is always the goal isn't it.
it is not for anyone else to criticise your methods or results. but finding things out as you go along is part of the fun.

I am not surprised by your findings. a little research has big rewards not for the purists perhaps but in any event worthwhile it is not always about more power or speed which is a good job as there is very little gain to be had without spending mega bucks that is totally lost on a 80's runabout.
if you spend some time researching the history of these bikes the manufacturing methodology and mindset of the designers you will understand how you can change things for little effort and money yet get the bike to suit your needs when starting out from a useless wreck to working best for you bike.
did you know for instance the engine in this (and other like models) started out as a 450cc that is basically half of a early 900cc 4 cyl engine bored to 454 and later 500. so yes half of the manifold from a 900 fits you can use either the right side or the left side depending on which side you want the can on. also almost any other Kawasaki part made for sportsbikes fit just fine. so any swing arm. wheels. forks brakes ect fit right on. just the spacers and fixings need changing. handy if you hate those 16in narrow gen 1 wheels.

the only thing I find surprising is you used ER500 cams (unless they were all you could get) they are far milder than the EX/GPZ cams produce less torque and power than the more aggressive stock ones.
anyway enough from me. well done on the completion of your project. a few photos would be welcome (we like photos)

 

[Peterex]

Thanks for the comments.

I will correct the errors in the article. When i bought the exhaust manifold i realized the kawasaki make gpz, gpx, family similar or the same parts so than i start searching in OEM part, and watch blueprint, and ofcousre read EX-500.com. After these researches i start modifiing the bike. I whrite these because i tried several carb jets, and needle jets, etc. so this is just the final and good mods. What i find good, and if someone else like to try it doesn't make damage for the bike.

I try an other one GPZ 500 1st gen with the original 60 hp camshaft, but its was more lazy in under 5000 rpm then mine with these modifications, so i leave the er-5 camshaft. (I have an other one 60 hp camshaft in the shelf) Usually i use my bike to go work and back in urban and suburban places, and under 6000 rpm, so its better for me. I can use 6st gear from 2500 rpm without any problem, but its more fun to use from 3500. Its very rare that i need more than 7000 rpm including passings.

I like the 16 inch wheels, With bar and weights the wooble of the handlebar was dissapears, and i can find cheap but good tire in these size. I forget 1 mod. Tire. I use different size than the Stock. Original is 100/90 16 inch front. and 120/90 16 inch in rear. I use 100/80 16 inch front and 120/80 16 inch in rear. Its the same wide as the stock, but lower, its make the tire less flexible in the side forces, but its better in corners, and these tire's have less weight, witch is give you less rotating mass. Better acceleration (rear wheel smaller diameter, same consequenses like smaller sprocket) and better brakeing.

Thank you for the comment again.

Pete

 

[yorkie]

hi. yes it is the cams carbs and cdi that makes the EX/GPZ the pocket rocket it is. it is supposed to be a screamer their not happy at low revs in high gears. I understand why you went for the milder ER alternative as that bike is a outright commuter bike. as for the 16in tyres there hard to come by here and the reason most go for the 17in version a lot of new 16in tyres are basically scooter tyres and not up to the job of holding the bike while cornering on full power at $$$mph.

 

[Peterex]

And the pictures. The bike is dirty. Its always dirty. Doesn't matter how many times i wash it, next day its get dirty again. Sorry.

 

[K-woppa]

Hello and welcome! You're obviously a serious motorcycle enthusiast. Good job on building the bike the way you want it to be. Thanks for sharing it with us.

 

[yorkie]

nice bike.

 

[bpe]

The bike is dirty. Its always dirty. Doesn't matter how many times i wash it, next day its get dirty again. Sorry.

Isn't that always the way. 😁

 

[Peterex]

Isn't that always the way. 😁

It's a GO bike, not a SHOW bike. Nice line.

 

[po18guy]

Welcome! Good work and good research! Too bad you don't like to rev the bike - the engine wakes up at 7000 and pulls strongly until about 9500-10000.

 

[Peterex]

Thanks! The engine still have the wake up at 7000 rpm, just the firework smaller after 9500. At lower rpm have better torque and linear performance. For me the 180 degree inline 2 engine have better sound lower revs.