I buy Seafoam once a year,to clean upper cylinder area.I insert a vacum line into the seafoam and let it slowly sip the can till all gone.I also change rpms while it running.
You can see it work if your cylinder area is dirty.There will be black smoke the first five minutes followed by white smoke(clean).

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt