Here at sea level 16-mm works well for me. I've always used the circle on the jet block to get in the ball park, then it's a wet check to verify. As a mechanic for many decades, I'm embarrassed to type how many times I took my carbs apart until I got them right the first time. It's well worth the efforts. Now I can get them spot on most of the time. Dannymax,Sean, Mark, and many more of you. without you guys I'd have struggled even more. This forum rocks!