Poor mixture distribution
1. Partially plugged fuel nozzle. A partially plugged nozzle will allow
enough fuel to flow at idle for combustion. As power is increased, cylinder
gradually leans out until detonation or lean mis-fire occurs. Exhaust gas
temperature will rise and not respond to mixture control until idle cut
off is reached. The reason for this is that the blockage now becomes the
primary restriction and is independent of mixture control position. Nozzles
can be flow-checked by comparing their outputs in containers of equal size
to locate plugged or partially plugged nozzle.
2. Damaged nozzle. A nozzle damaged from over torque will not meter
fuel properly. Damage caused by over torque usually effects the air-bleed
at idle.
3. Air leak into induction system.
4. Burned (leaking) exhaust valve.
5. Probe problem.
6. Inside diameter of fuel lines too small (Lycoming engines). Lines
must be between 0.85 and .090 inches I.D. Use of primer line instead of fuel
injector line. The only exception to this rule is the IO540 -E1B5 used in
the Aero Commander 500S. Fuel lines on Lycoming engines should have an
inside diameter of .085 inch to .090 inch.
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(Westach Probes at 1,200 degrees F.- 26.03 millivolt, at 1600 degrees
F. 35.24 millvolt)
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