this:
http://www.troybilt.com/equipment/tr...specifications says that your generator has a 420cc engine. Which is much more reasonable. Same model?
No wonder you expect it to keep up with your compressor.
Better be sure before someone tells you what size pipe to run. 420cc also happens to be almost half the size of your other(920cc) engine, which has 2 cylinders instead of 1, so the sizing is going to be close to the same. At a guess.
45 amps? at 120v? I sure hope you have a thick cord going to that thing!
Wonder if your governor is working properly...can you reach the throttle linkage to try and force it to open the throttle wider, just to see if it helps?