If the carb has the original settings, it is definitely set too lean. When you remove the air cleaner and provide a more free breathing exhaust, that automatically leans the mixture from the already fairly lean factory settings. Open the high speed needle at least one full turn and and the low speed about a half turn and try again. If everything else in the system is sound, that should let it rev up, and possibly be a touch rich. You can fine tune from there.

AV8TOR