How is the draw? Is there any significant change? I've read that even though you open up the outer airhole, the hole in the center pin will still restrict it.
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absolutely right. I take my r91 and kfl+ apart for cleaning quite frequently and the path the airflow takes is as follows:
1) through the airhole on the outside
2) through the hole in the center pin
3) up through the hollow centre pin
4) onto the deck (below the coil) at the end of the centre pin.
I've measured with a caliper (although i cant rmb the exact numbers).
- the stock air hole is SMALLER than the hole at the base of the centre pin. So yes, technically drilling out the air hole will increase air flow. BUT....
- drilling the air hole is only gonna make a difference up until the point where it reaches the size of the centre pin's hole. Any bigger and it's no difference at all. ** note that the initial difference is very very very small to begin with
which now brings me to another point. IF for some reason your R91 or KFL comes with a ridiculously tight draw, there is a chance that it's simply because the holes in the centre pin is not aligned with the air hole path to the outside. That's what happened with my second R91. Impossibly tight draw regardless of how i loosen the AFC. took it apart, realized that the centre pin holes were aligned such that less than 1mm of the hole was aligned with the AFC air channel. Aligned and slotted it in slowly, screw and secure, perfectly adjustable airflow as usual.