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Topic-icon Trouble shooting my rough running IO360

  • Baris Yildirim
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3 months 2 days ago #1508

Hi
The IO360 on my Arrow 200 lately developped some rough running issues at idle.
It almost always happens during the idle check at the end of a run up.. I captured this in my datalogs attached.
The log in #1 shows how erratic my EGTs get right after a runup, with cylinder nr1 EGT being the worst. Fuel flow drops to just about 1.3gph and the EGTs are all over the place. The log in #2 shows how the engine used to run about a year ago where everything is looking smooth and fuel flow at 1.7gph. Both logs were made with same mixture setting so I am not running it excessively lean in the first picture.

Full rich, fuel pump ON/OFF does not fix the problem. The only way to stop the roughness is to increase throttle a bit. I dont suspect induction leaks because the engine idles really nicely after a flight. Roughness only happens when the engine is cold.

any ideas what to try next for trouble shooting?
thanks!

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2 months 4 hours ago #1560

It sounds to me like it's "morning sickness" aka sticking exhaust valve(s). It's caused by build-up of deposits and/or corrosion on the valve stems. The valves can be dropped into the cylinder and a reamer passed through the valve guides to clear any build-up. Details are described in Lycoming Service Instruction 1425.

Have you had your magnetos checked and fuel nozzles flow tested to rule out an ignition or fuel issue? If not those should be checked first.

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