First thing, Most nelsons run on 15 percent fuel Like Powermaster or wildcat. Since you are using a after market carb, there will be little loss on the high end RPM. If the engine is an AAC version, You might try running the engine fat then lean it out til it just hits its last step on the pipe then go 1/8 turn ritcher. Once you go lean on a AAC engine it takes a few moments to go back to ritch because the liner takes a while to shrink.