Massimo msu 700 doesn’t want to rev up

[Kensei]

My brother-in-law turned it on its side  it ran fine before now after he did that is doesn’t want to rev up now

[Joe Breaux]

was it in water?  wet the electronics or wiring ?  check fuel line for obstruction  from trash in tank .. 

[ElbowRoom]

Depends what you mean by "doesn't want to rev up". If it barely revs faster than idle, it's probably in limp mode which means the ECU is protecting the machine by preventing if from rev'ing because of some error.  Since the machine was tipped on its side, it's possible that there is air in the radiator hoses, which is fixed by burping it: raise the front wheels at least 20 inches off the ground and idle the machine with the rad cap off while adding coolant until all air bubbles are out.