Nice bike.
It should be just getting warmed up and accelerating nicely at 70mph and ready for much more.
I'd suggest checking valve clearances and inspecting and lubing the timing advancer before looking at carbs, Carbs should be last. .If you do carbs first and then find the problem is valves then you are back to rebalancing carbs again after doing the valves.etc.
If you need a manual then the electronic one here is ok until you find a hard copy
mbsween.bike-night.com/kz750l3/manual.html
