Don't those wire-wound strings do a good job of reaming out precision-drilled holes to the wrong size? Use whatever solvent floats your boat to soften the deposits, but use only high pressure air to blow the passages clean. An instructor at the GM training center in Memphis used to say "Put 55 gallons of air through every passage!"
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!