chain/sprocket

hello I'm new to rideing and im haveing a problem with the wheel it will spin freely for 90% the chain will be very lose then it will get very tight and be hard to move idk what this means I was thinking it must be the chain itself any opinions? I'd love to hear them thank you

I am talking to a manufacturer about possibly making a 415 or 428 chain/sprocket kit for the RC 390. He said that we would need to get at least 20 people to buy in to justify the work and that the 415 kit could take a few months to produce. They could possibly get a 428 kit made up sooner. I...