Fuel pump arm rides on a lobe in engine. Try turning engine a quarter of a turn at a time to ease installation of the pump.Use an inspection mirror if necessary to see what I'm talking about. Good luck.
Just check all of the normal weak points; spark plug, condition of spark (blue) fresh fuel,etc. Worked on a twenty year old tractor, no spark, installed a new coil, ran great and mowed grass for a hour. The next week, would not start, fuel pump stopped working, changed that out and it's good to go. All you can do is keep the fluids and filters clean along with blowing out cooling fins when they get dirty. If you see something wrong when checking oil, don't ignore it! I find that if I show some TLC to my equipment I'm more likely to fix things quicker and then less big problems. Good luck and happy mowing.