ok read all the posts for your problem fix is simple... the xs 850 has thee carbs that must be in sync for the engine to run right ... you will need to find a set of vacuum guages... then remove the tank set up some way to get fuel to the engine... the connect the guages to the vacuum ports between the engine and the carbs. the start the bike. now use the adjustment screws on the trottle linkage to get the readings on the guages to read the same. you will be amazed at the performance improvement.