Expecting too much performance from G16A?

So I have a basically stock G16A in my "zebra" it was sourced from a local scrapyard and I was able to fire it up when I got it home.
It smoked pretty bad but otherwise ran fairly well.
I pulled it out, cleaned it up, did a nice hone on the cylinder to clean it up, installed new double oversize rings to match the double oversize piston it was already fitted with.
Cleaned and lapped in the valves, new crank bearings, new headgasket, new crank seals.
Cleaned the carb thoroughly, set valves to .008 hot as per a suggestion on here about plowmans performance recommendations.
Has a non stock air filter and a Honda cycle muffler installed.
Stock primary clutch in good shape and working smoothly, RHOX secondary clutch setup supposedly goog for increased torque, stock belt over 1" wide still.
Cart has a lift kit and oversize tires but nothing too crazy.
I can tune the carb so it pulls ok at low speed but then it suffers at higher speed,
I can get tuned so it will get up to a decent speed, but then it struggles at lower speeds and on hills.
Oh and the fuel pump has been cleaned and pumps well also..
Am I expecting too much power from a 301cc engine? I feel like it should pull better than it does.
Suggestions anyone?