Fouled spark plugs can often be cleaned to return some of their effectiveness. Don’t expect them to perform as well as brand new spark plugs, but cleaning will help them last as long as possible.
Fouled spark plugs can easily be rejuvenated:
1. Remove the spark plug and using a brush and clean rag, remove as much of the visible dirt and grime as you can
2. Then give them a soak for at least a solid week in a container of carburettor cleaner fluid.
3. After the soak, clean them off and reinstall, you should see (and hear) them.