A touch of Lycoming morning sickness

[Canuck]

My Lycoming O-320-D3G has always run rough for a couple of seconds after cold start, something I've attributed to the fact that only three of the four cylinders are primed.

This year, "a couple of seconds" have expanded to 10–20 seconds of noticeable roughness right after a cold start before all cylinders are firing evenly and smoothly at idle, so I'm not sure I can blame it all on priming any more—it sounds more like the infamous Lycoming "morning sickness."

From what I've read, a prime suspect is the valves. My next annual is in December, and I have a couple of questions:

1. Where should I ask the shop to look?
2. What is the best language to instruct them so that I maximise the chance of discovering any problems while minimising unnecessary and/or invasive work on an otherwise solidly-performing mid-time engine?

FYI, I do not have an engine monitor.

Thanks,

David

 

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[RickS]

 

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