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All of the above slides are genuine Keihin #7 slides for the PWK 36 Quad Vent Short Body. The left and middle can be purchased from Jets-R-Us for just under $70 per slide. The left (no-notch) part number is circled in yellow, and the middle (stock notch) part number is circled in red below. The one on the right was modified with a Dremel and conical stone bit.
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The no-notch slide is a bit harder to set a consistent idle. Air is only allowed past the bottom of the slide. The idle screw will have to be turned nearly all the way in, which will make the slide rest highest in the carb.
The stock notched slide helps set a more consistent idle by "broadening the range" of the idle screw. Some air is allowed to leak by before the bottom of the slide. This broader range allows easier fine tuning with the pilot air screw. This slide will sit lower in the carb than the "no-notch" slide.
The modified slide opens up the notch and smooths out the transitions for less turbulence. Larger notch means that more air will leak by before the bottom of the slide, and will sit lower in the carb than the stock notched slide.
The same pilot jet was used for all three and the idle screw was adjusted to maintain the same idle RPM.
The main point of posting this is to note the different heights each slide will rest at in the carb for the same idle RPM. This height will affect when the needle taper comes on in relationship to the PV opening point. Its my understanding that if the PV opens after coming onto the needle taper then you might have some blubber. If the PV opens before coming onto the needle taper then you might have a lean spot. I have to admit, that i do like it somewhat lean here. It feels like it cleans out easier, faster and is more crisp past this point. I tend to cruise between trails, or do longer flowy uphills holding this throttle position. It doesn't become a problem until the engine is really hot after a longer technical section, or installing performance parts. This lean spot is exploited and the engine will either have a slight run on after holding this throttle position, or make a clunky noise when really hot. So if the slide is sitting lower in the carb, either installing a needle shim or dropping the clip one position might help. I tried dropping the clip and did not like it.
Hopefully this helps. Jet-R-Us also sells 1/2 clip needle shims if really trying to fine tune.