My gyroplane has an EA81 twin carb engine that was overheated to siezure and has now been rebuilt but it runs rough and does not develop the power it should.
The rough running does not allow an idle below 1200 RPM as it causes the gearbox to chatter, previously it would idle down to 800 RPM. The engine seems to smooth out as the revs increase but the power is down as the new engine will not rev past 4800 RPM whereas previously it would go to 5400 RPM with the same pitch on the propeller. The engine was 700 hours old before this rebuild with compression significantly lower than has now been achieved.
The work done
Cylinder heads professionally machined and rebuilt, new valve seats, valves and valve springs
Cylinder blocks decked, bored 0.5 oversize.
New pistons and rings
Pushrods checked for straightness
Pistons, rods and crank rebalanced
Camshaft checked, it is believed to have been mildly ground in the past but I did not measure it up when I had it out.
Reconditioned carburettors with butterfly shafts bored and bushed, Hitachi carbs, float levels correctly set.
New sparkplugs, distributor cap and points, points were set with dwell meter.
New spark leads were not replaced as they were only 30 hours old. One lead measured high resistance and was replaced. All 5 leads were then exchanged with a set from another engine that is running well without improvement of symptoms.
New oil pump
Waterpump approximately 30 hours old.
Battery is 30 hours/12months old and in good condition.
Engine was rewired approximately 30 hours ago, some was heat damaged and repaired.
Spark plugs,coil and points have been replaced yet again in sequence without improvement.
Currently cylinder compression ranges from 175 psi to 195 psi.
There is no water in the oil or other indication of head gasket issues.
Ignition timing is set at 30° BTDC at 3500 RPM, this results in 4°BTDC at 1200 RPM (with vacuum line attached). Distributor has not been rebuilt but timing light gives a very solid and stable visibility of marks on the flywheel up to 4000 rpm, and was not tested any higher.
Valve clearances have been checked and rechecked at 0.25mm inlet and 0.35 mm exhaust.
I have sprayed carby cleaner liberally around all manifold and vacuum connections looking for a leak without success.
I have balanced the carburettors with a vacuum meter.
I have disconnected the carburettors one at a time and sealed the air intake forcing each carburettor to be the only carburettor in turn, no change in symptoms.
Carburettor idle solenoids were disconnected in turn with a significant deterioration of the idle in both cases.
I run the engine on 98 octane fuel with a valve seat protection additive.
The engine does not overheat when running.
Oil pressure is good.
I cannot hear any pinging or knocking but engine is run without a muffler so these would only be heard at low rpm.
Is it possible for symptoms to be caused by missaligning the camshaft by one tooth? Would the compression suffer if this error was made? I don't believe this is at all likely as I remember viewing the alignment mark through the large bevelled hole on the crank when reassembling but if somebody knows the symptoms of this error it would save some hair pulling on my part.
Otherwise I am devoid of ideas having replaced or swapped out everything I can think of.
Any suggestions out there?
Cheers and thanks