Is my motor bad?

[Polar_Bus]

So if you observed gritty debris on the intake and or carb venturi I about guarantee your engine is done. Maybe not now, maybe not in a month but the bottom end WILL eventually become trashed. I advise you DON'T spend money by replacing the top end as if you do, a few month(s) down the road you trash a crank bearing , the bearings will pass metal fragmented debris back up into your cylinder (remember 2 stroke air / fuel flow theory) and seize your fresh top end. My $.02 is to buy a long block and drive happy and not worry about a ticking time bomb. (as always just my opinion)

 

[Z.hb71]

I'd buy a zenoah longblock instead of rebuilding it tho, like Polar said