Golf R carbon build up - is there a cure?

Is there anything I should add to petrol to reduce the carbon build up on the exhaust in my Volkswagen Golf R? Or will it harm engine? There is a build-up on the exhausts. I sometimes use metal polish to remove deposits but I am concerned what it is doing to the engine. I want to make sure it does not cause future engine problems
The Golf R has Volkswagen's improved EA888 2.0 litre chain cam engine, which is direct injected but also uses indirect injection so that indirectly injected petrol can clean the carbon off the inlet valves. The most effective way to do that, and also to get the maximum power and efficiency from your engine, is to run it on Shell V-Power Nitro Plus which is what it was optimised and certificated on. Anything less gives you less power, worse economy and creates more carbon.
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