black smoke sounds like it may be runing a little too riche maybe overchocking that causes excessave gas consumtion loo kat the glass window on the carb at runing idle gas leval should right in the middle of the glass no higher would spray clean the chock e i used too set the mixtur with a portable tac very carfully turnin mix screw little ata time at a warm idletell eng starts too slow then liston and watch the tac as you turn it back out slow at a moment too stablez until you get toohigest rpm you can get on the tac if the idle speed drops you went too far then adjust the idle speed screw if the carb does not adjustgood may need rebuild black smoke is almost certainly a sign of too rich oil burning is usely blue smoke my twenty r minimax get 15to 17 had 20r wagen and truck get that stration out gas miles should a lot better i tend to forget young people maybe not familer wit carbs old like me not with computor lol