Last year (or year before) I bought an crappy 3HP motor, parts. I repaired it. At 1/2 throttle, it seriously sounds like it's above 3.6k RPM's already. Am I missing something? Another 3HP I have also does that... Half throttle and it's an beast...

Crappy ?? Tecumseh?? possibilities are, governor lever not adjusted correctly on governor bell crank, governor spring too tight, governor link not installed in throttle control , and I once inadvertently put governor link in wrong hole on throttle control.
???????

Thanks for the help. But it's an barn 3HP. Bought another carb and gave it another recoil and she was running... for the time being. It spitted out alotta rust from the muffler... so you can imagine how "barny" it was. But everything else was good though. Even my 2HP sounds like an beast... Might just be sensetive ears?