270-290 sounds normal to me.......but I run on grass. Do you? If you run on asphalt, the temps will go way down with the same tune. On dirt, the temps will be somewhere in-between.

Only thing I try to do is keep the temps under 300F to ensure it doesn't detonate. I've had an engine that hit pretty close to 400F once as I had it way too lean. It sure sounded odd, and I suspected detoantion, but no damage though.

The temp gun habit is hard to break, but if you can......try tuning without it. Tune the HSN just rich enough it doesn't scream and make sure there's a smoke trail.

If you can....leave the temp gun at home. You can always do the spit test if you have a moment where you are concerned.