If it chokes, starts, idles correctly, but runs poorly when you go to take off, the carbs are probably dirty. You can try a chemical cleaner product additive in the gas/petrol, such as Seafoam or Berryman B12, other options may be available. If a fuel additive doesn't help clean the carbs, you may have to pull the carbs to clean them yourself.
The temp gauge ought to go to about the halfway point, pointing straight down, maybe just a little bit more to the right if you're in a hot environment. If it is getting very close to red or in the red, you are probably overheating. The fan comes on near the halfway point.