Most carbs have a fixed air jet that lets air from the inlet bell mix with the main jet fuel before the mixture sprays through the needle jet below the slide.
The R models have the variable air jet (VAJ). It has three jets. The engine computer can open up one or two more air openings to lean out the mixture or close them to richen the mixture.
I think you could delete the vaj blocks, drill the carb out, press in a fixed jet, and block the hose fitting on the carbs but it may not run as well.