What fuel are you running the new byrons 30% has less but better oil content.I was able to get better run times ,had to lean about a 1/3 to 1/2 a turn on needle with my RB c5 same temps. More power throughout.More burnable content.
You didn't mention what temps you are running the motor at. An rb can an some times likes to run 250-265 put in a new plug run two tanks if it looks shinny still pobably room for leaning.Better than going totally lean on a straight running out of fuel. Google search" reading glow plug".Carb resrictors help but loose power. Lower nitro will boost run times, as well as hotter plug different brands can fill gaps between med /med hot ect.. I'm not up every plug. Track looks you could go 14 on clutch but doesn't always give better milage sometimes worse . Not up on all pipes or what is legal where you run but if you get a mid pipe you be getting more usable charge on that track packing more otherwise lossed fuel back in engine.
Are you balancing your wheels adds a little weight but the benifits will worth it vibration is wasted energy and unseats tires from surface.
Lightening up what you can.
RBs aggressive crank timing use more fuel.