i wouldnt buy a new gokart with a cruddy 150cc chinese motorcycle engine. plus they cost around 2,000. i would get one a used one off of craigslist
I happen to have one of the GY6 150cc clones, from
a 2008 scooter, that was wrecked, and sit outside for
years, I put a small amount of oil down the spark plug
hole, cleaned the bad gas out of the carburetor,
changed the oil, and it started right up, it has a fair
amount of power, feels like as much has my old Honda
185s ATC had, I am not saying it would have enough
power for a mini-dune buggy, but it's got enough power
to push me around at a good speed after I turned it into
a reverse trike, and I weigh 250lb, also there are a lot
of parts you can buy for it, plus a lot of service and
repair manuals floating around, it is a copy of a Honda
motor, so it has a good design.
The reason I say it may not have enough power for a
mini-dune buggy, is the weight of the mini-buggy plus
the weight of the rider, I think on mostly flat terrain, like
in the yard, down a dirt road, it would be just fine, but
hills and mud, I dont think it could handle it.
I am about to build a Granddaddy mini-buggy in a few
months, using a 16HP Honda clone motor, and a Comet
40 Series Torque Converter, its going to cost around
$1500 + or - in parts, I honestly think its a better deal
to build it your self, but not every one has a welder or
a place to work on a project like that, so I understand
wanting to buy a pre-made, and after messing around
with that Chinese scooter, I don't think that Chinese
clone motors, scooters, and such are as bad as people
make them out to be, or at least not all of them.
And if I had $1500 extra to blow on something, I might get
a Chinese ATV with that GY6 150cc motor, just because
I know its simple and easy for me to work on, and I dont
mind tinkering around if it messes up.
But like what others have said you might be money ahead
to look at your local classifieds and craigslist.