G1 running concerns

[کcяεαмιηĐεмση!]

hey guys(and girls if applicable) im new here but have been reading for a couple weeks and have put to practice alot of your good advice. my cart was given to me by my father, it was in poor shape but with some tlc to get clutches to move, a power kit and new helix from plowmans and pretty much cleaning of everything from top to bottom and it runs good. my question is this the top speed i have observed with handheld gps is 15mph on a 1 mile flat highway. it starts and runs good no issuses, fuel pump pulse is good and carb has been thoroughly cleaned. I'm in no way expecting nascar peformance but i hear of governor bypassed stock g1's running 20's at least but 15 is my max, and ideas where to start tinkering? i also notice that the last 1/4 throttle pedal seems to have little to no effect to overall speed/engine note. i have throttle adjusted to start cranking engine at proper time and move butterfly to WOT so i believe range of motion on cable is good(i feel like), ido intend to bbq pipe but will that really rob that much mph?