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With the exhaust mod, the bike starts running very lean again at idle and at top speed, to the point where it's almost the same as before the whole O2 sensor delete.
This due to some of the restriction of the exhaust flow being reduced through the larger exhaust holes.
This mod unfortunately is kind of irreversible, unless one can weld some material back and make the holes smaller again.
In a way, my exhaust is now reacting like a freeflow exhaust system.
So if you want to put an aftermarket exhaust on the bike, you'll also experience the bike running way too lean.
In a twist, or turn of events, I found a rather simple solution to the problem, going back to restricting the flow a bit at the header.
Using the M12 x 1.25 bolt in the O2 bung, I can now dial in how rich or lean the bike is at idle and at high rpm, regaining my top speed, as well as reduce idle heat, and reintroducing a bit of low end torque.
Though this will also result in riding a bit richer in the mid throttle range, and affect mpg.
In other words, if you have done the same to your bike, or run a crf230 exhaust, you'll need to install an o2 sensor bung in the exhaust, close to the exhaust port, and use washers under a bolt to set the bolt height and control how much you'll restrict the exhaust flow.
With my current setup, I am restricting the exhaust tube by about 10%, which feels like the perfect compromise between torque, top speed, and mpg at cruising speeds.
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