Matt,
  To be helpfull, we'd all need more info on your engine,prop, mixture setting when the engine roughness started.  Sounds like a plug problem, or a EGT probe/wire problem perhaps..???  Not knowing more than your post I wonder why you choose to run way over squared, MP vs RPM..???  The engine garus will probably despute this, but I don't run that far from MP/RPM squared, at any condition (climb,cruise,or descent) say 2300RPM & from 21 to 25" MP, and ALL power changes are made slowly...My 320 Lyc seems to purr more often.. 650 hrs on a 0-320, compression on all four was 78/80 last week.. Regards  Don Skeele  A&P
>
> From: "Matt Hapgood" <matt.hapgood@alumni.duke.edu>
> Date: 2005/06/01 Wed AM 11:47:03 EDT
> To: "Lancair Mailing List" <lml@lancaironline.net>
> Subject: [LML] misfire
>
> I had a problem on a flight on Saturday that I have never had before.  The plane is just out of annual.  I made a one hour flight at 25" x 2400 RPM.  Approach asked me to descend relatively quickly.  I pulled the power back to about 21" x 2500 RPM and the engine started running rough.  I noticed the #4 EGT at zero.  I pushed the MP back up and it cleared up.  I pulled the RPM down to about 2300 - 2400 and it cleared up.  Just leaning the mixture didn't solve the problem, nor did richening the mixture.
>
> This was the first annual where I have NOT replaced the plugs.  Instead, an A&P just cleaned them (they are automotive Iridium plugs).
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> I have electronic ignition and electronic injection.  Was it a clogged injector?  Not likely, as it cleared up at higher MPs and lower RPMs.  Was it a spark problem?  Not impossible, but it would have had to kill both plugs.  Were the plugs fouled?  Not impossible, as #4 is my richest cylinder.  But the problem happened later when I tested it, after I had been running for 20 minutes LOP.
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> Unfortunately, I tried to get it to happen again on the ground and, of course, it won't repeat itself (at about 20" and 2400 RPM).
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> Any thoughts?  I'm going out to decowl the plane and inspect the plugs, but I'd appreciate any thoughts as to what to look for.
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> Matt
>