The left foot T140 gearchange can be a bit stiff, which is mostly due to having that dirty great big cross-shaft going across the engine, as I belive the gear selector springs had to be made stiffer to cope with it!
My own '78 model T140V's gearchange also feels somewhat stiff when compared to other bikes I own, but it does feel much better while riding than it does when trying to select the gears without the engine running for instance, but it shouldn't be so bad that you have to stamp on the gear pedal to change gear?
Try and seek the opinions of other left gearchange T140 owners if you can, and see if they think your gearchange is the same, or worse than theirs?
If you do decide to look inside the geabox, then the Haynes manual information given for the 5-speed gearbox is completely misleading, and I don't think they have bothered to correct it in any of the later Haynes T140 manual reprints over the last 30 years, even though they have had ample time to do so!
