Yamaha produced the FZR1000 from 1987 thru 1994
EXUP (EXhaust Ultimate Power valve) A device fitted to selected Yamaha motorcycles (FZR,YZF,XV1900,R series) that constantly adjusts the internal diameter of the exhaust system to suit engine revs. This ensures good low to mid-range performance for a linear power output all the way to the rev limiter. This is achieved by using an internal valve (similar to a butterfly valve) inside the exhaust at the point where the four pipes from the cylinders meet. Closing of the valve then creates a venturi effect inside the exhaust system, causing an increase in pressure on the engine side of the exhaust system. This increase in pressure results in greater exhaust velocity. A servo motor controlled by the ECU opens and shuts the valve. The EXUP valve operation goes from being almost fully closed at idle speed, through to being fully open at 9000 to 11000 RPM (2500 RPM for XV1900).
Float valve height = 13.5mm - 14mm
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