Using big valve means allowing for more air and fuel mixture to enter the combustion cylinder for more power delivered to the crankshaft. As usual, any modification that relates to increasing the power (hp) of the bike will increase the fuel usage.
This original Yamaha 135LC head is coated with copper. Why? This copper coating comes stock from the factory. It is used to make the slip much more heat resistant and also scratch resistant. When the valve got bigger the stock slip become much more thinner, so copper need to be adhered to the valve seat for protection against heat and scratch.
Available for sale here
26 more pictures after the jump
All of these images are courtesy of syark86. Find him here