put the shim in, i always do for brake in, plus with the shim it should not pre-detonate with th 33%. as for keeping it running you can do it the way jazzy said with the idel screw or you can just keep it running by working the throttel with your finger on the radio. both ways work, but most important, you must keep the temp above 180 degrees but not higher than 220. you can wrap the head with tinfoil.