Dual spring exhaust valve linkage assembly

In an exhaust valve having a valve plate connected to a shaft located crosswise within an exhaust tube, the valve plate and shaft capable of corresponding rotation relative to the tube;

• the valve plate having first and second portions, the second portion having greater surface area that the first portion;
• an improvement comprising a linkage assembly including:
• (a) a crank arm connected to one end of the shaft;
• (b) a first elongated link having a leading end protrusion and a trailing end with a trailing end protrusion;
• the trailing end of the first link being rotatably connected to the crank arm at a location distal to the crank arm connection to the shaft;
• (c) a second elongated link having a leading end with a leading end protrusion;
• the leading end of the second link being rotatably connected to the exhaust tube;
• the second link being located parallel and adjacent to the first link with portions of the first and second links overlapping;
• (d) a first spring positioned about the overlap portion of the first and second links, between the leading end protrusion of the first link and the trailing end protrusion of the second link;
• and
• (e) a second spring positioned about the second link between the leading end protrusion of the first link and the leading end protrusion of the second link;
• wherein the linkage assembly includes a neutral position in which the first and second links are generally transverse with the crank arm, and the first and second springs bias the links and the crank arm to the neutral position;
• an open position in which the crank arm is rotated to move the first and second links away from one another, causing the second link to be less compressed than the first link;
• and a back pressure position in which the crank arm is rotated to move the first and second links toward one another, causing the first link to be less compressed than the second link.