Thanks, you guys, for your input.
Good point, Chopperpilot, about the vacuum feed! I didn’t fit the tank myself but I had a manual tap on the OM tank so it was already blanked off at the carb.
The few comments about fuel consumption could get us into a long discussion that’s probably been gone through many times on this forum.
I spent 4 days, last week, doing 2000 km in the E Tvl. Two 700 km days getting there and back, and two 300 km days riding dirt roads and passes. No problem with fuel consumption on the slow days but I thought it worse than before on the “hanging on the cable” days.
It’s 50 years since I studied physics but I believe, for turbulent flow, that wind resistance is proportional to the square of the speed. Increase speed from 100 to 110 and wind resistance will increase by 21%. Which is why I think a less aerodynamic tank could meaningfully increase fuel consumption at higher speeds.
(Seconding my son in a canoe race, I carried a spare split shaft paddle with the shaft halves sticking up out of a backpack. At 80 km/h the wind resistance on the two 25mm shafts was no problem, but when I tried to speed up to 100 I felt in danger of being ripped off the bike.)