All of the sudden in July my fuel consumption on my 35B engine climbed to between 0.8 and 0.89 gal./hr.  In 15 years I've owned Talisman it has been consistent between 0.6 and 0.64.  This is measured by actual gallons replaced and engine hours on instruments.  No other change in behavior noticed and no change in use patterns.  Engine starts immediately and runs as beautifully as always.  No fuel leaks in bilge or diesel smell in the boat.  No change in exhaust fumes.  Boat is out of the water now and bottom was pretty clean.  Even though the numbers are low I'm concerned about the engine itself it has 2100 hours on it.  I would assume if injectors, valves, etc. in the engine had problems I would notice loss of power, noise, starting problems, vibration or some other sign not just increased fuel consumption.  This is about a ⅓ increase in consumption or about a quart per hour.

it has been suggested my hours counter on my tachometer is off effecting my calculation.  Has that happened to anyone?  Can it be fixed?  If the counter fails I would think it would just stop working not just slow down.