Ok, most def a 125 is too small for you, 250cc is about what you need, If your looking for speed get a 2 stroke engine with a power band and a jetted carb. If your just looking for something to ride casually and you don't want to show-off on it, get a stock 4 stroke.
Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.
I'f your just starting out riding dirtbikes and don't know how very well DO NOT GET A 2 STROKE.
Start out with a 4 stroke or you might kill yourself, fast dirbikes are very dangerous, I know from experience.
other than that a 125 is too small for you, I have a 250 and I'm 5'8'' 155lbs.
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