Engine Vibration with high Manifold Pressure

[BigTex]

While out flying today I detected a vibration when the manifold pressure was at 25" or higher.  When I backed it dow to 24" or lower the vibration went away.  Changes in RPM seems to not have any effect.  Also tried playing with the mixture and carb heat with no change... Thoughts?

[jetdriven]

Engine monitor? EGT's change?  Perhaps a dirty injector, and adding MP adds fuel pressure, which causes a larger power imbalance? wild guess.

[BigTex]

No monitor but EGT on #3 is slightly elevated until the engine is leaned out.  No injectors on this engine.

[jrwilson]

Mine was a little rough recently.  Was at 8500 feet and mp was about 22".  The egt had an approx 75 to 100 degree rise on #2 cylinder, no change in cht.  I wasn't sure what it was, hit carb heat and richened it slightly, and the problem went away.  Egt came back down to normal.  I checked my JPI troubleshooting manual and it said I had dirty spark plug on #2.   

Problem hasn't returned. Egts were normal the rest of the flight.

[jetdriven]

Do a mag check inflight with the mixture at the leanest setting you can get.  Report back.

 

[BigTex]

Will do... I was doing some stop and goes before climbing out where I experienced the roughness.  I plan on checking the plugs as well.  I might have a fouled plug as well.