Hi everybody

I just installed a new muffler and o2 sensor. the engine is running pretty
well but performance seems a bit off. previously about a month ago I had a
mechanic adjust my timing, valve's, idle and CO etc. now that I have put on
a new muffler which seems to have less backpressure and a new o2 sensor. the
engine runs pretty well but does not want to pull hard at the higher rpms
and seems to pulse a little at higher rpms. my question is..... which
adjustments should I need after these changes???  it would seem that timing
would not need to be adjusted again. how about CO? are there any adjustments
that I can make on my own or should I have a mechanic check these??

thanks for any help.

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