Adding to what rustypep said about metal to metal...Muffler on solid? Rx been in a crash?Crystal in tight(72mhz)? Antenna routed properly, not doubled back( 72mhz)? Switch harness good? Tx and Rx batteries, plugs and leads in top notch condition? Long carbon fiber pushrods touching?(if used). Engine block to motor mount clearance present? Prop in acceptable balance? Tx antenna tight?