My recently bought a low mileage 1982 450 Honda seemed a bit gutless. Before taking the carbs off to clean out the old gunk I thought I would try using some Seafoam . I poured about 1/4 of a bottle in the tank and forgot about it. This morning when I took the rig for a spin the difference was immediately noticeable, it really flew. At best I was hoping to see an improvement over a hundred miles or so, but not straight away.
I have to say that it is not the type of engine I'm used to, it thrives on revs compared to everything else I have. I previously read that a solo CB 450 was good for 110 mph / 180 kph, but did not believe it, I believe it now. It's easily fast enough for use on the highway. I'm going to give everything I have a dose of Seafoam now.
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Just think...if 1/4 of a bottle of Seafoam was good for 110 mph/180 kph, then a full bottle of Seafoam should be good for 440 mph/720 kph 
My wife's slightly newer 1986 Honda Rebel 450 also got the Seafoam treatment, as well as Marvel Mystery Oil in the engine oil.
Been a Seafoam and Marvel Mystery Oil user for half a century.
Two Million Mile Rider
Exploring the World in Comfort