After completing my annual condition inspection and 5-year rubber replacement, including carb diaphragm, some but not all carburetor O-rings, new fuel pump with new O-ring and gasket, new sockets and manifold-to-socket O-ring (fuel lines not included as teflon), the engine test run revealed very rough engine that could not run above 3400 rpm.

Steps I have taken so far:
    1.  Pulled a plug from each cylinder
               a. #1 plugs black with soot
               b. #2, #3, and #4 all clean
     2. Repeated compression test: all four still 79/80 or even 80/80
     3. Because I had to remove R-side intake manifold to get at coolant hose clamp, I suspected an air leak at #1 cylinder manifold-to-cylinder O-Ring, so I replaced both R-side with new O-rings, new bolts and washers.  Also replaced #1 cylinder spark plugs
     4. Repeated engine test with no change - still very rough, still sooty plugs only on #1
Here is what I did in replacing the coolant hoses plus annual:
             Removed carbs and sockets
             Replaced carb diaphragms
             Replaced the O-rings on the top of the jet needle
             Replaced idle mixture O-ring
             Replaced idler jet O-rings
             Decided not to replace all of the rest of the rubber parts in the carbs out of an abundance of intimidation
             Weighed floats - all were good
             Replaced carb bowl gaskets
             Inspected gascolator and fuel strainer back in June - did not repeat
             Cleaned air filters
             Complied with Van’s SB 00026:  Addition of retaining plates for throttle springs, including new springs.
                           NOTE - I have not yet rebalanced the carbs but the throttle cables were never touched. 
             Replaced all coolant hoses.
                           Spilled some coolant onto ignition module at one point.
              Oil and filter change  

Related info

  • Compression in all 4 cylinders 80/80 (checked three times, twice after rough engine discovered
  • Fuel is new auto gas  91 OCT alcohol free (always)
  • Fuel pressure is normal with electric fuel pump on and off
  • CHT temps normal.  Right side is 6-7 deg F lower than the Left
  • EGT normal and equal
  • Oil pressure 50-60 immediately on starting and during entire engine tests
  • Did not check mag differential during test run
  • No fuel leaks anywhere
  • No coolant leaks

Do the lower CHT on the right suggest it is running richer than the left?
Next steps?  I am suspicious of a carb problem on the right (starboard) side.

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