The front of the engine is the worst place to aim your IR gun at.
Try to get access to the spark plug base. Paint it black! Aluminum reflects the weirdest readings unless the surface is black. Take good care in reading the included angle when measuring. The smaller, the more accurate.
When measuring the spark plug base using a small angle IR device pointing at a black surface, you should see readings of about 180°C to 200°C in a well tuned engine at full throttle static. The back of the cylinder topmost part should be about 150°C, but is almost impossible to read using the IR gun.

All in all, an IR temp gun is quite difficult to get good readings with, and for that reason is near to useless unless you know, and adapt to it's limitations.