4 stroking at low speed

The standard jets on the factory carbys are way to big IMHO usually .68 ,my suggestion is to go down to a .65 and see if that helps

But we really need more info such as jet size the oil your running and the type of carby ( I suspect the NT )

There can be only two main suspects in my oppinion and they are jet size and fuel mix .
Being a newbie you can get somewhat daunted by the carby adjust but it's simple ,I always run in my motors at 25:1 and general running after breakin at 32:1 ,you should find if you are running the kit recommended mix ,swapping down to 25:1 should somewhat fix your four stroking issue ,40:1 for breakin is IMHO way way to low to be any good for the motor

Try these and get back to us with your results

Regards Hen

Wait until u get at least 100 miles on it before u start messing with it, but I would go with a 24:1 mix until 100 miles

300miles would be better before trying to tune it - the older speed carbs were about 2mm larger in the venturi than NT - didn't make them horrible on the standard engine setup, but they worked better with an expansion pipe - I currently see a newer ver of the speed carb being sold now, but don't know what has changed

Yeah, if price were king, these would be in the royal family.