Re: engine choices
The one thing in your question that makes it difficult to answer is the word "kit". The reason I say this is because the best engine out there may not necessarily come from a kit. Of the two choices for kits being two stroke or four stroke, I would personally recommend a four stroke. No mixing oil and gas, and really all you need to do is check your oil, change it if its dirty or low, keep your chains lubed, perform proper maintenance on your gearbox and clutch, check your valve adjustment, and make sure you dont abuse your engine by over-revving it for extended periods of time. The 2 strokes can be made reliable, but they require proper tuning or they wont last very long at all, and with the poor quality control at the factories where the 2 stroke kits are produced, there is no guarantee of how long even the best cared for engine will last. Now, if its a 2 stroke you want with decent power, a ktm/morini clone is the answer, but those do not come with a kit and require fabrication to mount to a bicycle frame. There are also a few options for non-kit 4 strokes as well, for example Lifan, Predator, Honda, Briggs, others. It really depends on what you want to use the bike for, what kind of performance you want, what terrain you are going to be riding on, and how much you are willing to spend to get what you want out of your bike. I've done the two stroke kit thing, got tired of it, and recently spent about $800 to build a custom bike with a minibike engine. And there are guys who have spent two or three times that much on their own custom builds. All things for you to consider while deciding.