We have tested needles many times with, lets just say, extra large mains on Mikuni carbs. The Keihin has a slightly different taper style needles but the principal is the same. The area we need to be concerned about is where the needle leaves the jet needle. There is never a common answer with jetting as we all ride in different conditions and styles etc. Your dropping your mains huge ,I guess, because the carb is on a different engine? That means the main was wrong so if the needle was set up for the other condition then it is probably wrong as well. Also depending on the carb design flow. For example, carbs like the Keihin (some only) and the TMX and TM American are set to run with a rich mid and lean top end. You will find the TMXx from Japan on modern day bikes have a very lean mid range and rich top end. As an example our YZ125 would run probably about a 160?? with a PWM or American Mikuni but would be hard pressed to get under a 400 with the Japanese TMXx style carb and the pipe we use. In testing – we have gone from a 460 main to a 390 and dropped the needle (leaner) by two clips as well!!! Again – with our setup and our style and our conditions. So – it’s really good to hear you are into testing but there is no magic setting or standard. With the old VM’s or even the TM you can change that rich / lean % at will (with experience) but not with your carb. If it was me I would simply drop your mains and set the needle couple notches richer and ride it and make changes. If someone’s paying the bills – leaner out till she seizes then go up one – but it’s safer to start rich and work down. Bob Hogg PS – how come you dropped so many sizes? :cool: