[Gr8NW]

I had an issue with loss of power and eventually changed plugs to solve the problem. All worked fine until I drove at idle speed for about an hour then same problem and brand new plugs fouled. Looks like lots of carbon build up on 3/4 plugs. Any suggestions as to what might cause this?

[rodbolt]

wrong grade fuel,excessive oil, failing ign system components,bad thermostats, incorrect throttle linkage set up,poor compression.
fouled plugs are a symptom something is failing not a failure.