He is correct about the no-start if the intake valves are worn closed - check valve lash to fix. However, that WON'T cause the initial problems as you described them. If I recall you said initially it would idle but was not revving for s**t.
Check/adjust the valves then go back to troubleshooting the original problem.
'01 660 Raptor, Burgard +2+1 arms, YFZ Shocks, LSR anti-vibe, CTR pipe, jetted, K&N
'01 Polaris Scrambler 400, K&N
'02 Honda 400ex, Big Gun pipe, jetted, K&N, Lonestar +2 A-arms, Lonestar anti-vibe
'04 Suzuki LTZ400
'16 RZR XP4 1000 Turbo