2003 250, I ended up w/ this quad on a trade deal, I know nothing about it's history other than it got a new carburetor put on it last year. My problem is that it will run, but only w/ the choke fully out, and it runs abnormally fast regardless of idle screw position. If I try to slowly push choke off, it starts to sputter and then blow-back pressure damn near pushes carb off the manifold. I see where timing in NOT adjustable. I have taken the carb apart and checked all jets, needle valves, etc, both diaphragms are good. Everything still looks brand new. I'm stumped on this one...or is this a carb issue??

 

See what the pilot screw is set at.Item #9. http://www.bikebandit.com/oem-parts/...5679#sch258295 If it's at least 2 turns out from a lightly seated position, having to have the choke on usually means somethings either stopped up,set wrong or something else wrong such as float level off,needle and seat sticking,fuel supply to the carb restricted,etc.

 

Thanks polaris Tech, have messed w/ the pilot, found that it was originally set 1.5 turns, backed it out a hair more than 2 turns, tightened up the intake clamp, and seems to be better, I can now get it to idle w/ choke off...it's still needing something, it has a hesitation on accelerating and sometimes will drop below idle speed and get that back pressure before dying.
A.) smelling old gas from exhaust, going to empty this trash fuel, check/clean tank, replace those petcock filter "socks".

B.) replace / gap a new plug

I just got this thing Sunday and have been messing with it during rare off-times, surprised it started actually. Will report back my findings after doing the above, perhaps tomorrow.
Thank you sir

 

If you're smelling gas then probably time to replace the needle and seat and check the float level. Usually these old Mikuni float arms are suppose to be parallel with the carb bowl when held upside down. You can pay 16 bucks for an oem needle and seat or cheaper just to get the kit that has a lot more.http://www.ebay.com/itm/CARB-REBUILD-KIT-YAMAHA-YFM250-BEARTRACKER-250-1999-2000-2001-2002-2003-2004-YFM-/370503176178?hash=item5643b5cff2&vxp=mtr

 

yes, I may...I just did another one of these that way (gold,250 B Tracker), bought a rebuild kit from china, (flEabay) for 22$ it did the trick. May do it again, I dont see where this carb needs it, everything is looking great, been taken care of. Will be a last resort
thank you sir