I have a blue 253 and took everything off that I thought was tacked on polution stuff. But tracked down a rocky service book. And it explanes what everything for. So put it all back on, the only thing I did was to cut the snorkle as close as I could to the exahust bypass flap to just increse the air intake opening. Haven't had to ajust anything for the last 10 years. The biggest thing was to perfect the auto choke and the fast idle speed at start up. The best thing is to have the manifold heat stove/ flap working properly when cold, makes the motor warm up so much quicker. Do you self a favor and get a service book.