Seems my rides in Malaysia are popular and people continue to ask where to rent a big bike in Kuala Lumpur.
One answer is The Big Bike Shop in Puchong. I have rented there and they are good guys. They have a variety of rentals, helmets and jackets too. I took a Kawasaki ER6N pictured here.
Unfortunately their web site still seems to be offline. Jump on Facebook where you can find them and send a message.
Update – I have been contacted by another shop in Kuala Lumpur, Klez Bike who rent Harley Davidsons one of which being a XR1200 which would be quite nice machine to ride in the Cameron Highlands and they also have a Kawasaki ZX800.