I've had this quad for some time now (2007 Yamaha Big Bear 250)... It hasn't been running in about a year and a half. I just bought a new carb, petcock, fuel line and filter, and a new battery. So I got it started and it is revving at wide open.. kinda scary.. I would let it run approx. 5 seconds or so and it never went down so I shut it off. One time I put it in gear and it went around my yard a couple times but I could tell it was still wide open and then it cut out. When I give it gas it kinda bogs down... I checked all my boots and vacuum hoses and didn't see a crack or leak. I've heard of lean runaway from a thread and I filled up the gas tank half way as a precaution. Now I am thinking I should do a complete rebuild on the bottom end and all new gaskets, valves, valve seals etc incase of an air leak.. If you would have any suggestions before I do this I would appreciate it.. I am no pro mechanic but I am learning! I really want to get this running before Halloween so I can pull the kids around on the trailer like we have done years in the past.. Thanks

 

A lean condition would not make it run wide open, so it sounds like you have an issue with the throttle cable or linkage. Something is holding it wide open, I would think you need to go back over your installation of the carb.

 

i have the same machine also check that idle adjust tends to stick or freeze go over your install on the carb and throttle also remove that side plate for the throttle cable and check have done extensive work on this machine ,,, good luck