If the break-in run can't be completed without stopping and tinkering, somebody didn't do his homework right to begin with. A little valve rattle isn't going to create any permanent damage, so I add .002" to the "hot" valve lash setting and leave things that way until the initial run is done. Ditto on ignition timing- - - -tweak it by ear for the best sounding exhaust note and press on. Running at no load, it's virtually impossible to get any detonation damage, even if the timing is advanced a little too far. Use a squirrel cage blower on the radiator, or just run a garden hose over the outside of the radiator if a little extra cooling is needed.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!