IF you are thinking of tinkering you need the shop manual - the spec is there - I run mine at 1000-1100, generally the lower for the fatboy and the higher for my e-glide (more electrical draw with all the geegaws since the alternator output is proportional to the rpms). I've always heard that 1000 is a minimum due to oil flow requirements.
1000 on the Low Rider. Adjustment is on the top right of the carb when viewed from the right side. There's a spring on the screw. Do it when the engine is hot or the RPM will still be high when the engine warms up.