|The jets have numbers stamped on them. There is a book "How to Build and Power Tune Weber & Dellorto" by Des Hammill. It does a good job covering how the carbs work and lists all of the available parts. I read it 3 times but still can't figure out how to tune a Dellorto, but I keep trying. I have added an O2 meter, which I think is pretty important if you are not a "carb whisperer" ;) Very small changes to the mixture screws which don't seem to do anything to idle speed or audible engine running affect the mixture big time. You see it on the o2 meter. Of course there are mechanical issues in the carb that can cause problems also. The book goes over all that as well.