First thing you should do is purchase the clutch lever mod from Jim at
Manic Mechanic Sick Bike Parts have a teflon coated clutch cable that helps as well. This will solve the clutch problem on your 2 stroke.
As for the 4 stroke: I don't have one myself but my understanding is that the Hoot brand gearboxes are pretty awful unless they are tweaked by someone experienced. Shims and hardening of certain gears seems to be required. The Hoot gearboxes look like the number 8 but on its side. The Grubee gearboxes (oval shaped with flat sides) are supposed to be much better but there are several versions. You will want the most recent. Other than that there are other companies that are in the process of bringing out new 4 stroke kits (different gearboxes). 2 that come to mind are Firebelly and EZ motorbikes. Both look very promising.
I went back and looked at the 2 kits. I purchased a motor from Kings several years ago and I had no problems. However the 4 stroke kit they show does not display the transmission in the first picture. If you go to the description tab and click on the bigger picture link it shows you an engine with the Hoot gearbox. For this reason I would avoid this kit.
The other link in your thread from bicycle-engines.com used a Grubee gearbox so I would go with that one if I had to choose between the two. Yes it is more money but not really. Purchasing a kit with the Hoot gearbox is like throwing your money away in most cases. Much better to get something that will actually work. The Firebelly and EZ motorbikes transmissions both sound like they will be the best yet. I have heard that the EZ motorbikes kit will sell in the $650 range.
