Regarding drilling jets. I have rarely done this, preferring to get the size I wanted from the carb source; though I realize that's not always possible anymore. I have read that aside from orfice size, the shape of the jet's inlet affects the fuel flow.
Recently I've dealt with Amal and Mikuni motorcycle carbs, whose jets are stamped with the number of cc per unit of time (Minute?) so an idle jet stamped 20 flows 20 cc and a main jet stamped 160 flows 160 cc. Needless to say, the #20 idle jets plug up with silt that gets by the filters or whatever and have to be cleaned out. I use a gas-welding tip-cleaner and/or a dose of spray carb cleaner.
There are tiny orfices in automotive carbs too, particularly in the idle and transfer circuits within the carb body, and emulsion passageways. I don't remember about Rochester Bs but some enulsion jets have a whole raft of tiny radial holes and a very tiny orfice at the end. When these plug up, off-throttle hesitation is often the result and part-throttle leanness also results. The residue from ethanol mix gasoline plays the devil with these.
I have also read on various blogs I follow that one can't read plugs anymore like in the days before no-lead and ethanol laced gasoline. 'Tis said that the insulators will always be white because it was the lead that created the color. I don't know what to believe but I've not been successful at reading the plugs on my two Zenith 228 carbs on my stovebolt. Plugs are always white. I've seen lots of color on my Norton motorcycle engines that burn no-ethanol premium. I'd like to hear any opinions on this subject. But I don't want to hijack the thread either.
