March 22, 2014 11:13 AM PDT
I'll try to offer some helpful advice on the subject.
Changing pipes/ air intake:
It's all about air flow. If you change just your pipes then no changes to air/fuel are needed because air is still flowing at the same rate. The rate of airflow only changes when the intake is allows the air volume to increase.
The bikes ability to compensate for changes in the air flow is limited. The bike is designed to adjust air/fuel mix for outside air temp, altitude, air flow, engine temp, etc... but these changes are all based on a stock intake/exhaust. When you change that dynamic without tuning the bike you will cause the engine to run lean.
HD already sets the bikes to run a little lean in order to help comply with emission requirements so, not adjusting the air/fuel mix to compensate will cause the engine to run very lean. This can effect performance and engine life. When you consider that an air cooled engine requires fuel to act as necessary part of engine cooling, it becomes clear that running overly lean can present issues.
Aftermarket A/F tuners VS SERT:
There are advantages and disadvantages to both.
The SERT is adjusted using HD software so, it must be tuned at a dealer. It can only be assigned to one bike and cannot be reprogrammed for use on another. However, the big advantage to the SERT is that it can do more than just A/F mixture. It can adjust spark timing and allow changes to sensors.
Aftermarket tuner {Power Commander, etc...} will allow for adjustments in A/F ratio but not much else. Although they can be reused.
If you are simply changing intake, exhaust and maybe a mild cam adjustment then an aftermarket A/F tuner is a good choice. If you are planning on engine mods or drastic cam changes a SERT is your best bet.
Carbs:
It is a common belief that carbs do not need to be adjusted for air intake. This is not really true. Although later model carbs can adjust for changes in altitude and minor intake changes fairly well, if you make large volume changes to your airflow you may become dangerously lean. It is important to engine life that engines are not run in an overly lean condition. I personally rejet every card on a bike that has intake modifications.
LEAN ENGINES RUN BALLS OUT!
Overly lean engines have a tendency to seem as if they are performing better than a suggested A/F will and they do. Racing engines run very lean.
LEAN ENGINES HAVE SHORT LIVES!
The important thing to remember is that although short term performance may be improved, the engine life is going to suffer. Race engines run extremely lean because there is another engine available for the next race. They are not meant to last. Don't confuse a lean condition for a good running engine.
Dyno Tuning:
If you want to get the most out of your bike have it Dyno tuned. It costs more but is worth it. There is no way to get the best A/F ratio without it. That being said. Power Commander does a pretty good job of providing reference material to get your bike fairly close without a Dyno and the O2 sensor system seems to work pretty well if you spring for it.