5 minutes was just about long enough to just get it warmed up, but not long enough to even begin checking the spark plug just yet.
Your spark plug is not indicating anything as you have not ridden it far enough or long enough.
Try that one again but give it at least a half hour this time.
As far as top end speed is concerned, I have never seen it where those poo poo exhuast pipes do any good whatsoever in that department, you would actually get more top end with the stock pipe...A smaller rear sprocket will also help out for better speed but its a trade off as you won't have as much low end torque.
Also, is that an after market head or the one that came with the engine kit???
Change your fuel mixture as well to 25 to one mix ratio for the breakin period which is about 100 miles or so which means about two tankfuls of gas and mix your gas and oil in a gas can, not just in the tank as it will not be consistantly mixed that way...It has to be done in a gallon gas can and shaken vigorously in order to mix it properly and then pour it into the tank, and be sure to be using Conventional oil only during break-in period...NO synthetics until after break-in.
If your using the Chinese spark plugs that come with these things, throw it out, they are garbage as well...Most of us here change them out immediately to an NGK-BR6HS spark plug gapped at .025 thousandths.
I never even checked my plug until the first 300 miles or so once everything was fully broken in as well as running a couple tanks after that and this is what my plug looked like which is about the best perfect burn your gonna get.
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