Power control valve attachment for two cycle motorcycle type engine exhaust systems

A power control valve attachment for assembly to a pre-existing exhaust system of a two cycle type engine for increasing the power output characteristics thereof, said exhaust system having a back pressuring chamber including an outlet duct section of a given predetermined minimum internal cross sectional area of the exhaust system duct section for effecting a given back pressuring of the engine cylinder chambers during operation of the engine, said attachment comprising:

• an assembly of pressure plate means for sensing the pressure of exhaust gases flowing out said duct section and biasing means for biasing said pressure plate means against deflective movement under pressure of said exhaust gases, said pressure plate means including a tubular member having an open end, a side wall including a plurality of ports and a closed end closed by a plate having an outer diameter larger than the internal diameter of said outlet duct section;
• means for mounting said assembly in a slip fit relationship to said outlet duct section with said tubular member extending into the open end of said outlet duct section, with said biasing means extending into said duct section and with said plate being exteriorly and biased toward said open end of said duct section;
• and
• means for retaining said attachment in assembled relation to said duct, whereby said pressure plate means tubular member and plate are movable under the pressure of exhaust gases from a duct section closure position wherein said plate abuts and closes the open end of said duct section to variable back pressuring positions wherein portions of said tubular member protrude from said duct section open end and said plate is axially spaced therefrom.