You must have gotten lucky...
When I was on the track with my (then) stock Tokico's and RCS19 pump, after two laps I could pull the brake lever absolutely onto the handle, and the brake force wasn't there..
When the brakes were "cold" the brake force on the lever meant you could NOT pull the lever onto the handle, unless doing it with two hands. So there was some MASSIVE brake fade going on.
And yes, the calipers were serviced not too long before.
(fixed the problem now with Nissin calipers from a 07/08 ZX-6R and Brembo HPK 320mm discs)
I believe the reason that after 2 laps your levers reached the handle is cheap brake pads.
Additional reason would be an unlevel disc (if you uninstall the disc and place it on a plane, no light should pass under it.
If your brake were that hard that you could n't pull the lever after the bike got cold, I believe the problem is actually 3 or at least 2 of these:
1) your brake pads side springs (pins) are not missing but they are broken and do not allow the brake pads come back properly.
2) your brake pads mounting springs are deshaped or broken and do not allow the pads to move back
3) (it might or it might not) Your rubber sealing has been damaged and some of its damaged parts are now in the space behind the pads and prevent the pads of moving back compeletly.
I believe your problem was solved after you changed to Nissin and Brembo discs as well as other members change their calipers and the problem was solved.
What I believe is the problem here is the fact, that the OEM parts that you guys changed had cheap pad, broken parts in the brake calipers, and the system was not bleeded just like "Johns04ZX10R" mentioned.
You guys are lovely. I knew i forgot something. I just didn't know what. I forgot several aspects that without them you won't get perfect flawless front brake on you OEM brakes. Those 2 aspects that i forgot to mention are:
1) Brake pads themselves
2) Brake rotors
3) Brake lever
Do not install the basic brake pads on your calipers. First of all not only they don't last long but most importantly, most of the braking force goes into melting those cheap pads instead of stopping the bike. Go with the med or advanced version which has seramic and other metallic and pads from tougher materials. They provide great braking and they last longer and provide less amount of pollution every time you brake (see friend of environment here :) ).
Most speed vehicles have a protective layer on the rotor to protect the surface of the rotor and provide more firction that with a burn out pads and having the ribbits of the pads rubbing at the rotor, those layer would get damaged. If you are planning for a heavy speed race you need that layer unharmed on your brake rotors. For regular street use, just service your brake system and you do not need that layer.
One very important flaw in rotors, is the fact that they lose their shape or they are not level at first to begin with like ALL brake rotors from our lovely producers in China. having an uneven rotor mess up your whole race experience, they create heat, they rub your brake pads and can damage brake system parts.
Many times in races they brake rotors on fourmual 1 cars turns red not becasue of the driver braking too much but becasue the brake rotor lost its leveled condition and is engaged at all times.
A leveled brake rotor is a rotor that if you place that rotor on a plane you should see all the parts of the rotor sits on that flat plane.
Now, for the brake lever, You wont believe my statement until you actually experience it yourself. If your brake lever is a cheap brake lever -might look good or not- it does not provide the true power of your brakes. Buy an OEM brake lever for 2005 or 06/07 from Kawasaki Dealership and install them and adjust them with a tight grip (1) and you understand what i am talking about.
Note: Do not buy OEM brake lever for gen 1 or gen 2 on Amazon or online because they look almost the same as the Actual OEM but their difference to OEM is sky to ground. ONLY and ONLY buy your brake lever from Kawasaki Dealer.
I had installed 06/07 and 2005 brake OEM on my bike and they are both excellent.
Someone mentioned on cold weather, they experience tough braking on the brake lever...
Well, i believe that you have a problem in your brake system or you just think this is April and trying to joke with me. I have ridden in under degrees celicious (the temperature that regular water freezes) and brake lever is just fine. The temperatures under 30 degress celcius are so cold that public regulation encourage people to stay at home not because your brake fluid freezes but because our body freezes.
Your brake fluid does not freezes or -even thicken so hard- at our regular cold riding temperature. They get thicken very very slightly.
Now, to all riders:
Your healthy brake lever tension (even at the toughest grip adjustment (1), is smooth enough that if you have the bike parked and attempted to pull the brake with your pinky finger (smallest finger) you can with effort. I don't have crazy bulky fingers but still can with some might effort to pull the front brake all the way in with my pinky finger. I have do it easily with all my other fingers without might effort (with DOT 4 and with Adjustment (1)). So if your brake levers are hard to pull there is a problem somewhere.
The improvement area:
The rear brake on first gen is very weak and emprovments in my opinion is necesseriy if you are planning to race. I have seen stunt riders add another caliper and join that with the orignial caliper for better stopping. In my opinion if you are plannign a race (speed race) it is better to provide additional cylinder and reservoir within the additinal caliper and not just the cliper joined with the OEM.
For the frount if you are planning a heavy race like a Moto GP, i do recommend 2 different seprate brakes on front for each caliper (2 reservoirs as well). The bigger rotor with more intelligent strengened material, bigger brake lines and tougher pads, are all recommended.
I believe in a heavy race like a Moto GP the Original brakes on first gen will fail due to pressure and temperature.
* Every aspects in this post and other posts that i mentioned is based on my knowledge and experience that i actually performed, investigated, and achieved.
I did not copy any other post.
I did not even support someone's idea unless i actually investigated or tested that on my own and reach the same answer.