advice please, possible fault with yamaha pw250 motor

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Pedelecer
Nov 12, 2015
124
58
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Hi all, wondering if anyone can help diagnose possible fault with Yamaha pw250. I have a Winora radius 2016.

It has three gears. Gears three and two work fine. However in gear 1, as hard as I pedal cannot get over 13 mph. Going up slight inclines takes an awful lot of work now. Before this bike had no such problems. The bike is now pretty use less for any hill now :( Wondering what the cause could be?
 

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Pedelecer
Nov 12, 2015
124
58
49
Any Ideas on this peeps, I know it sounds a bit odd, maybe it more mechanical then motor related?