or if not mentioned,you can use break cleaner/carb cleaner,carefull though ,just incase,but if air is detected,as posted,revs will change,but got slow ,so you notice the rev change,if rev change is noted,there is your air leak,just same as water/washing liquid,,also ,if you have compressor ,you can make your own vacum tester,as i did ,with half a bean can,inserted air line,into hole i made in bean can,inserted bean can were tmic goes ,on pipe,and let a little air in at time,and listen,just another option,but guys who comment ,above me,know there stuff... :0)
ive also ,heard of those smoke pelets ,that u can get to detect gas vapour leaks also,for fires,people use those to find air leaks