OH ITS A 2 STROKE, wow i completely neglected to notice that, MY BAD. youre right there won't be an oil fill. yeah that ratio is important!
good thinking pulling the carb apart, that pin is called the '[mix] needle' btw (real complex huh - youll notice a lot of this shits like this, quite straight forward).
well that's a relief, saves you the time and effort trying to buy and fit a new motor. those motors I mentioned wouldn't just bolt on, you would've had to fab a mount for it and some sort of transmission to the wheels (easiest thing to do is weld a sprocket onto the axel and use a chain).
congrats! youve been learned motors. theyre really easy to tinker with, just dont break anything lol.
sidenote: if you're real curious to see the actual health of the engine, get a compression gauge. don't wanna get balls deep in the project only to watch the engine slowly lose power and die. the engine is back up and running so honestly I wouldn't really worry about it, but like I said im meticulous so I like to know these things. readings should be like 120-170psi. Super simple to use. Just take out the spark plug, put the gauge in, hold the throttle all the way open and rip the starter cord a few times and see when the needle stops climbing, thats your measurement.
(I am not a shill) I got this one and it works pretty well.