Loss of engine power when using lights

[Grasshopperus]

that's the new one, right?

The attached pic is the old one, it's got some sort of flakey rubber mark around the side closest to the camera. Looked pretty shagged.

I reckon (fair bit of experience here with learner bikes that need work) that its in your very best interests to check your oil for any signs of water, and DO go get a compression test to see if any one cylinder is noticeably down on the others. I'm not a fan of the guys at drury (who sold you the bike and how much for?) but as has been said earlier, head gaskets are cheap to replace, heads/cylinder blocks are not, nor are all the bearing surfaces.

Sure thing, I'm going to take everyone's advice and drain some of the oil tomorrow and take a good look at it.

Cheers for the help all.