The stock FC3S has a built in overboost fuel-cut system to prevent you from overboosting.  Please ensure that you're not hitting this overboost fuel-cut!  This can eventually harm your engine.
FC3S Pro - FAQ, Overboost Fuel-Cut

Problems with the ignition system can cause an erratic or weak spark.  This could be caused by a weak electrical system (i.e. alternator, battery) or bad ignition components:  spark plugs, spark plugs wires, etc.  Checking the electrical systems for proper voltage levels and replacing spark plugs and spark plugs wires can help.

A bad TPS can also cause high RPM hesitations.  If the full-travel specifications is outside of Mazda spec of about 6.0kΩ.  Replace the TPS if yours is over this Mazda spec at full extension.

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