150cc fresh built from ground up with +2 stroker sounds almost like its knocking..... What could cause it? Could it be piston slap? Only thing not new is the case halves. Runs like a top. Kinda stumped.

Is there any difference in the knocking when it is cold or warmed up?. Does the knocking follow the rpm (more when faster)? Grab a small metal pipe and listen through it as you touch it to various parts of the engine. Should act as a doctor's stethoscope and hopefully you can tell what part of the engine the knocking is coming from.

Did you use a spacer with the stroker? Maybe you need higher octane fuel now

The knock sound stays the same cold/hot and at idle/wot and yes i used the spacer. I started with 83 and now has 93 octane and it didnt change. The piston that came with the cylinder(58.5) had to much material below the wrist pin so i ordered a hoca piston which cleared the couter weights. So maybe the hoca piston is just slightly smaller than the bore?

Does it idle fine?

Idles fine and runs like a raped ape. Has an initial sputter when you first get on it but the carb is just one i had laying around.

take the vari off and see if its just the motor

check the starter clutch nut, it may have came loose