The thing here is that boy go fast does not manufacture the engines that he sells.
He's just a drop shipper and all of the engines and kits that he sells are made in china.
The reason that boy go fast has mixed reviews is that an occasion lemon of an engine will get sent out (this happens with all vendors who sell these kits.) but his customer service is not very good. But, if you didn't buy the engine kit from him, you won't need his customer service anyway.
Almost all china 2 strokes that are made for bicycles are the same engine (altho they are all built in different factories). i have bought several engine kits from boy go fast and i have not had a problem with any of them.
The key here is how well was the bike built and maintained?
How well was the engine installed, is it done right? Look at pics of assembled bikes here to get an idea of what looks right. If the bike has a hole drilled in the frame for the front engine mount, it can cause the frame to crack.
How many miles does it have on it (approx.)?
Does it have all of the stock original parts on the engine like the spark plug, exhaust, spark plug wire, air filter.
If it does, you may want to consider upgrading / modifying some of those parts with better ones (this can be done fairly cheap). There are a ton of things that you can do to it to improve the power, performance and longevity.
The stock exhaust can get clogged up with oil over time, reducing the performance of the engine.
Is the wiring done good? (all stock connectors removed and all wires soldered and heat shrunk? Wires not hanging all over the place?
The majority of failures to bikes with these chinese 2 stroke kits is due to incorrect installation, incorrect oil/fuel ratios and no maintanance.
$300.00 is fairly cheap, providing that the bike/engine was built right, looks good, runs good, isn't worn out and has been maintained.
A brand new engine kit from boy go fast (or any other e-bay vendor) will set you back around $120.00 - $140.00 depending on who you buy from. A bicycle itself can set you back anywhere from $100.00 -$300.00 alone depending on what you want. Then you have to figure in the time it takes to install the engine kit because most of the time, you have to modify something to make them work right. You should figure on a weekend to get one of these bikes assembled if you have never built one, or have very little mechanical ability and limited tools.
Make sure that the bike itself is good, no loose bearings, wobbling wheels, bent wheels, broken spokes, good brakes, etc.
if the bike is good, the engine runs good, is installed correctly (or what looks to be correct), and the wiring is good, then i'd say you're safe.
BUT, sometimes with these engines, you never know when they are going to develop a problem because they are all cheaply made, and they are basically throw away engines (altho they can be re-built if needed).
So look at it this way. You could buy this complete, running rideable bike for $300.00 vs. the hassle of ordering the engine kit, finding a good bike for a decent price and then assembling the whole thing. You'd still have probably around $200.00 - $300.00 in one if you built it yourself.
The chance you'd be taking with buying a used bike is, how long will it last once you get it?
Unfortunatley, no one has an answer for that.
you have no idea how the previous owner rode it, maintained it or assembled it.
