My son has a new 50cc atv. He has had it for about 2 months now. I have the throttle governed down to about a little less than half. It gets up to about 30km/h on a straight run(if it is long enough) I removed the governer to make sure the bike was running well and he took it up and down the street a little bit. It was definately alot faster but it was sputtering at high speeds. I put the rear end up on a block and tested it out. It seems that at 3/4 throttle it hits high speed and starts sputtering. I am not sure if this is top speed but it seems to me that something isn't right. The bike was sold to me as bushbear 50cc but I have seen it on US websites as a crossrunner 50cc. From what I can tell it is manufactured by loncin and sold as crossrunner( USA). Not sure if this helps but who knows. Any way if anyone knows anything about this type of atv and can help me out I would appreciate it.

 

I have no specific knowledge of that bike but I would bet it has an electronic rev limiter on it...You may be able to unplug it or it may be built right into the cdi box...If you have a spare spark plug you could try that but I would bet that its an rpm limiter causing the problem.