Friend, I'm not a specialist and I don't even know your engine, but there are simple procedures that must be followed before exchanges.
Swapping parts at random has little chance of resolving.
Generically ...
1 - Is the battery fully charged?
No - Charge it
Yes - next step
2- Is the spark of good quality (whitish blue)?
No - check the spark plug, see excessive carbonization, electrode spacing, insulator break, coil (open or shorted) and magnet (loose or broken)
Yes - next step
3 - Is there good quality gasoline in the carburetor?
No - change the gasoline,
Yes - next step
4 - Is the engine drowning or no gas in the chamber?
No - next step
Yes - check the internal parts of the carburetor, check for blocked fuel or choke, misfit or missing screws.
5 - Does the starter run normal or slow?
Normal - next step
Slow - check the voltage at the starter inlet while turning. If 12V or so, next step. If absent or much smaller, check starter relay and / or starter coil and / or oxidation in the cable from the battery to the starter ... the same for the ground loop on the chassis and battery negative.
6 - Are the intake and exhaust valve settings correct?
No - readjust
- next step
7 - Are any belts or something weighing the engine?
No - next step
Yes - disengage the weight or loosen the belt, see the oil.
8 - Are there any strange noises on the engine?
No - next step
Yes - if you understand, open the engine and solve or take it to a mechanic shop.
Note: there are motors that lead to other analyzes, such as sensors, protection devices ... but in general the previous steps avoid unnecessary changes.