Al – not sure I can help you with your kart carb, maybe though. I ran a Ford V8 flathead 15 years ago with four “Stromberg 48s” modified to run methanol and had four more “Stromberg 48” bodies modified to run 100% nitro. The Stromberg carb function similarly to your kart carb via two emulsion tubes with changeable jets in the float bowl. The Stromberg 48 also has a mechanical power valve that operates in conjunction with depressing the accelerator pump to help tune as well. Stromberg power valves were available in #50 largest, and #73 smallest.
Carb versus mechanical fuel injection tuning is not similar. For your kart carb to run methanol and nitro, at a minimum, you’ll need to increase the jet and emulsion tube diameter, and also tune by changing the power valve. I’m not sure how your kart carb’s power valve works, but that could present you tuning problems if it’s unchangeable. You should also modify your fuel feed line by increasing the inside diameter and improve the fuel inlet needle and seat to increase flow to your float bowl. Possibly locate a larger needle and seat to replace your stock one. Raising your fuel level slightly in your float bowl may help, but may not be possible with the design. If you have opportunity to upgrade to a larger cfm kart carb to modify for nitro, you may consider that move first before you modify your present smaller one.
Again, this information may or may not help you, but my Stromberg 48 jet area was increased 2.13 over stock to change from gas to methanol fuel, and 6.25 times larger area for 100 percent nitro. In other words, stock .048 jets for gas, .070 jets for methanol, and .120 jets for 100% nitro. At a minimum, you have to increase the emulsion tubes inside diameter percentage to match, and keep increasing or decreasing until you find your best setup. My setup used four carbs in a row, the engine was modified 286ci versus the stock one carb 221ci. From my perspective, your idea is excellent for learning, actuality for 15% nitro with your kart carb might be marginal. Alan