(JFLEISC) wrote in message ...
Since the last time I had posted the question about the roughness between 1000
and 1700 RPM my wife had taken the plane on a cross country flight and claimed
things seemed worse. Sure enough the roughness seemed worse plus the idle
(below 1000 RPM) was no longer smooth.

There's another little-known factor that sometimes affects these
small Continentals. On the O-200, at least, and perhaps the O-300
(been too long, don't remember) the carb is mounted on a "spider," an
intake manifold that is held to the case by two studs and nuts. The
Marvel Schebler/Facet Aerospace/Precision Aeromotive carb doesn't like
being shaken side-to-side as caused by rotational vibration from power
pulses, and can slop fuel from the bowl into the vent, which is in the
carb throat, flooding the engine somewhat and causing rough running at
certain RPM ranges.
So Continental calls for "Lock-O-Seal" washers, (rubber molded
inside steel) to be installed above and below the spider on both
studs. The nuts are to be tightened finger-tight only, with a wrench
used only to take the nut to the next flat for cotter pin
installation. They want that carb to flex side-to-side, with the
rubber intake runner connections keeping things centered while
allowing the flex.
We had an O-200 that drove us crazy for three weeks until one of us
finally read the assembly manual and the lights came on.

Dan