What brand of kit
ThatsDax sells a .81 small 10 tooth sprocket.
This sprocket will work on wall-e-world 1 to 3 speed BMX chain. You will need two BMX chains.
This is a total replacement of a cheap small sprocket and a cheap chain.
I bought a Kings motors kit and fought the chain until I repkaced everything.
You need to contour the old sprocket to match your chain if you just want to fix the Chinese junk that came with your kit.
I tried this and did not like the fuss and bother.
You will spend as much on a dremel or files as replacing the chain. LOL
I agree with spad the kit chain is junk. I replaced my chain with #41 chain. Much better, stronger, cheaper. $15. for 10 feet at Tractor Supply Co. I dont know where you are since its not listed but possibly a small engine shop would have it to....