Well it is hard for me to tell if it is going rich or lean, though I strongly suspect lean on the high speed needle. How many turns out is the high speed needle adjustment? If it is in the four turn or more area, you probably need to raise the lever in the regulator about .015". That will help the carb deliver more fuel, and get you rich enough on the top end. It is fairly common to have to do this on Gas/Glow setups.

I think, and this is just a guess with the limited info I have here, that your low speed was rich, and helping to make the high speed rich enough. When you got the low end dialed in, that leaned out the high speed until it doesn't have enough fuel to run full throttle. Unlike glow engine carbs, the low speed needle setting affects the high speed mixture on these Walbro and Zama carbs.

If you raise the lever in the regulator, you will have to start over with your needle/mixture tuning.

AV8TOR