Sounds very abnormal for a 140 -- not something I have seen so no definitive answers.

Sounds possible that the low/medium jet is fine (rich at low revs as they tend to come), but leaning out at high revs. One area I have sometimes had problems is with blockages in the carby jet. Blow the needle valve both ways just to make sure if you haven't already. Pull the carby barrel out (remove throttle stop and pull sideways), pull out the jet and blow all that out to. I can't imagine it is the pipe causing that kind of problem (unless you are using something very obscure).

Do others know how to check the pump?