wobbley

Hello everyone, I have a Fuel injected 07 YBR 125. It's been working fine all the way through the winter without so much as a blip and now the weather has warmed up it's stopped working.. It will start and run fine in the morning when the ambient temperature is cool but when I want to come home in the warmth of the afternoon it won't start. It turns over and I've tried to check that there is fuel reaching the injector through the fuel pipe. I've noticed that the fuel pump doesn't whirr when I turn the ignition on but yet it does in the morning when it's cold. What that is heat related is stopping my fuel pump working? Any help would be great. Thanks Richard