When you install your new jets, start the bike and get it warmed up. Then adjust the idle speed just a tad lower than normal. Then adjust the idle fuel screw...turn it in until you hear the speed start to drop a bit...then turn it out until you hear the the engine smooth out and the rpm's increase just a bit. If you have to turn the screw out more than 2.5 turns....or if you can turn the screw all the way out and the engine idle doesn't change - they put the #50 back in and try again. Mikuni claims that the correct pilot jet size is the one that will result in the smoothest running at 1.5 turns out on the idle mixture screw. Because of the tendency of the big single to pop and bang when you close the throttle, it is best to have the pilot jet a bit too rich rather than a bit too lean. If you can turn the idle mixture screw all the way in and the engine still runs....then the pilot jet is too big. (There is a bypass circuit around the idle fuel screw that will still allow fuel flow even when the screw is all the way in.....the idle mixture screw is the "fine adjustment". Too big of a pilot jet and the bypass circuit allows enough fuel for the engine to run even with the idle fuel screw turned all the way in). Then set the idle speed back up to the recommended 1,000-1,100 rpm.
Once you have the pilot jet sized correctly, take the bike out for a full throttle run. In a high gear with the throttle wide open....pay attention to the way the bike feels. If the bike pulls strong - but feels like it speeds up a bit as you roll off the throttle, then the pilot jet is too big (that won't happen with a #145). If the engine feels like it is surging and accelerating a bit unevenly...the jet is too small. Another good way to test is to find a straight section of road, and uphill is good as it takes longer to accelerate....and find a telephone pole or sign as a landmark. In high gear at 40 mph roll on full throttle as you pass the sign and accelerate to another landmark down the road and note your speed. Then put in the next larger size main jet and repeat the test...continue going to larger main jets until the bike actually gets slower, accelerates more when you roll off the throttle, or you hear the bike blubbering as if the choke was on. When you find the jet that provides the fastest speed...that is the best jet for performance, and for best mileage you may be able to back off one jet size and still be OK. Maximum efficiency is obtained at 14.7 pounds of air for each pound of fuel - while maximum power is obtained at around 12.5 pounds of air for each pound of fuel...once you get beyond 13 pounds of fuel per pound of air the engine is too rich and the power begins to drop off. That explains why you can jet for power...then drop a jet size for economy and still not be too lean.
Finally the adjustment of the slide needle. When you first start to open the throttle beyond an idle, the slide begins to raise the tapered needle and provide fuel flow. With the stock white spacer on top of the needle the engine can run too lean at low throttle settings. My bike had a very noticeable surge when you would roll on the throttle and ride away gently. I had done the 3 washer replacement for the white spacer, and I tried removing a washer and I ended up with only 2 washers and the surge was gone. I was then able to drop the main jet size one size and the bike ran great.
My bike had the best performance and mileage with a #50 pilot, #150 main, and 2 washers on top of the slide needle.
Here is a video of how to adjust the idle mixture screw. Once you have backed the screw out 3 turns - it no longer provides any additional flow as the needle is no longer restricting the flow and the hole in the carb is completely open. The screw ideally should be out 1.5 - 2.0 turns at the best idle - if the screw is in farther the pilot jet is too big, and if the screw is out farther than 2 turns the pilot jet is too small. I have attached an image that shows the idle circuit....and you can see the screw only controls the fuel flow out the second hole - the other hole that bypasses the mixture screw is only adjustable by changing the size of the pilot jet.
This is a long - but very good video.
https://www.youtube.com/watch?v=zm5mB3R8Ucw