Main Motorcycle: Triumph TR7
Join Date: Feb 2012
Location: Norwich, England
Other Motorcycle: T140
Extra Motorcycle: Most of another T140
I found the same with T140s - they do like free-flowing 'zorsts. As you say, 5000 is the powerband - certainly was on my old T140s. My current TR7 has a powerband at just over 4000, on almost straight-through TR6C type pipes and E3134 profile exhaust cam.
It may be wise to check the plugs - my T140s needed main jets increased from 190 to 230, then to 240 & finally 260 with the final stage (32mm carbs, no air filters, straight through pipes, 9:1 pistons).