its 49cc
. the clutch has 3 engaging sites with springs at each one it looks like. its exactly like the one is this video
Ok, so you need to get yourself a caliper and measure that shaft. You will also need to get a clutch puller just in case it's tapered. If it isn't, at least you were prepared. When it comes to tools, there is never wasted money unless the tool is ridiculously expensive, like a certain spoke threading tool sold on Amazon....$400, what are they runnin, a highway robbery ring? Anyways, you will also need a torque wrench, some shop rags, and a soft bristled brush to sweep away all that clutch pad material.
Ok, once you have all your tools, you can go about pullin off that burnt up clutch. To do that, just follow the video's instructions at the beginning and end. Skip all the case stuff unless you want to do some internal upgrades, like replacing the apparently plastic cam gear...plastic? Like, what is PLASTIC doing in such a critical area?
Once you have your clutch replaced, its time to do some preventative care. Check your gear ratio. To do this, count the teeth inside the gearbox, dividing the large one by the small one, and then do the same for the output sprocket and wheel sprocket. If it doesn't reach at least 14.0, your gearing is too high and your clutch isn't engaging. If you've got the stock 44t, up it to a 52. In this case, it's better to go too low in gearing than burn up another clutch. It is also a good point to be able to ride the thing while also diagnosing fuel delivery. Poorly running, your engine should be able to do about 18mph with a 52t, 20mph when running right. At that point, you can start experimenting with gearing.
One other thing, and this is important:
make sure there is no oil leaking around the shaft! Any present oil will make the clutch slip under power, generating a lot of heat that will anneal the springs and lock the clutch. This is what is known as heatlock, and is pretty well known around the 4 stroke community.
If anyone else knows any better about these little things, now would be a good time to pitch in.