I would go with the 48cc Grubee GT-2 kit from Bikeberry. This is the FIRST new engine that I have ever dealt with that started on the first kick. Quality was better than expected, even though I replaced most of the fasteners , NGK spark plug and dumped the crude steel intake manifold for an aluminum one. Installation instructions were decent, but I'm not a novice with mechanical contraptions. No leaks and runs like a top and very smooth. I'm breaking it in at the recommended 18 to 1 mix, but will switch to Lucas semi synthetic after break in. I also had to get a Poo Poo pipe because the stock cat muffler would not fit my setup. The Poo Poo setup did require minor tubing modification for the Schwinn Del Mar I have. I highly recommend Bikeberry.