there is no way in hell to look at an engine and access it's condition.
I've seen engines that smoked badly, leaked oil more than an old Harley,
and knocked like a Diesel, yet ran properly.
The only real way you will know the condition is tear it down.
Me, I'd get an inexpensive coil and see if it runs better.
Also you could have a bad "new" carb that you mentioned you replaced.
They all ain't winners out of the box.
Did you try the original carb?