RPM's all over the tach

[N171TD]

At 1200rpm R @ L drop 100rpm and very rough ( this is normal ? )
1700rpm both R L tach indicates no change ( sounds the same )
At cruise 2400rpm L @ R indicate an increase in rpm and a smoother running engine -- switch back to both then rpm drop and engine runs rough
Is it just that the timing is not at 26 and 28 as the book says ?

[davevramp]

First this is not normal, something is wrong. Really need more information to take a better guess. But a wild guess is weak mags or miss timed mags or engine timing. Had a similar problem when I lost a brg in one mag and it would act funny at some rpm and not others. But the indications would lead me to do more investigation in the mag area.
Good luck
Dave

[GAHorn]

I can think of several scenarios that might give such results but the information supplied is insufficient to diagnose the problem. My first thought is mis-routed high-tension leads (wrong wire to wrong spark plug) but it's also possible to have stripped distributor gear, carbon-tracking, or several other issues.
Quit running the engine until the mags have been inspected and re-timed, and the spark plug inspected and compression tests run on the engine. Those items will find the problem. (Although there is a very remote possibility of carb or fuel-air mixture issues, I don't believe that will be it, however.)