wont start after replacing head gasket?

[Dibz]

cam sprocket is SPOT on, lined up with the mark on the INSIDE of the sprocket (unless there's two marks?)
the accelerator pedal is not as high so that cable needs tightening up.

[rubjonny]

check the cam is in the right spot with the pulley lined up, it is possible to fit the cam sprocket on the wrong way round! The lobes on #1 should be pointing up and away from each other, like this |\  /|
Also shine a torch down #1 to visually check  piston 1 is at the top of the bore at TDC.

As dan says take all the plugs out and clean them up, had similar problem with a polo i did a head gasket on. after i cleaned the plugs it fired up right away!