I hate to jump in here, not being the most mechanical guy on the list...I
would say I'm somewhere near the 1475th least mechanical, in fact.
However, if you are running a large cog with an older derailleur (say a 28
tooth with a Super Record) and your skipping is on the smallest cog it may
just be that you have had to run so much chain on that larger cog that all
you need to do is move your wheel more to the rear. Simple fix if it
works...if one really wants to get into the more complex stuff like
experimenting with grinding on the teeth on the freewheel I have an even
simpler fix...this involves taking the dratted thing to my buddy's bike shop
and letting his 40 years of experience come to the fore while I drink coffee
and shoot the bull with the guys there...a lot less frustrating to me and
often even cheaper than me getting in over my head. I sure am lucky to have
such a resource!
I realize that there are folks who really enjoy knotty mechanical
problems...I sure am not among them. :^) Guys like Dennis Young (who pours
his own Babbitt Bearings!) really fill me with awe.
Tom Sanders
Lansing, Mi