A little background first. I've done a lot of things to my car since I purchased it and within a few weeks of each other, I upgraded to a Spec 1 exhaust, installed new fuel lines, spark plugs, plug wires, rotor and cap. Sometime after that, I noticed a hesitation or stutter when accelerating after the car was warmed up (driving for about 10 mins or so). The stutter is most noticeable when accelerating in the 1800-3000 RPM range but once I'm above that range, the car seems to even out and accelerates fine. Car is rock solid at Idle when cold or warm and stays right at 750 or so.

I'd read somewhere that after installing a performance exhaust like the Spec 1, some sort of adjustments might need to be made, but for the life of me, I can't find where I read that anymore. If I should make adjustments, can anyone point me in the direction of what I should be adjusting? I'm assuming it's just the mixture, but I'm scared to touch that as I've read that should always be the last thing you touch.

I recently acquired a Dwell meter and the following video shows my results as the car heats up.



TL;DWatch -- Cold, I get a steady 45 Dwell reading. 3 mins later the reading oscillates between 35 and 45. Approximately another 7 mins after that, dwell oscillates between 40-48 and another 10 minutes after that, dwell oscillates between 44-48. On both the last two readings, it seems like the dwell wants to stay at the higher end of the oscillation longer (hard to describe but video shows this). Disconnecting the O2 sensor or pressing the WOT switch gives me a steady reading around 48-50.

These readings seem to indicate issues when the engine is warmer, but seems to be correct when it's cold or just warming up.

Any recommendations given all of the above information?

Thanks,
Bueller