I was riding my xplorer 400 yesterday and it kept bogging down and stalling at mid throttle position. The only way I could keep the quad going was to open the choke. I thought possibly the vent to the fuel tank was clogged. It was not. I checked the lines that ran from the carb they were not clogged. I have noticed that there was fuel dripping out of the bottom vent line of the carb a few days ago. I had rebuilt the carb about a year ago because of dripping fuel out of the carb. Any ideas why the engine/carb was starving for fuel?

 

Was it rebuilt or just jets cleaned?? Sounds like you're gonna have to go back into the carb again! Especially if it only runs better with the choke on! Even if you rebuilt the carb a year ago and even if you have some kind of stabilizer in the fuel, a lot of times the fuel just gels up and plugs up the jets.Worse if you don't have any preservative. Could need the needle and seat replaced also unless you are able to clean it up without damaging it! Probably the source of the dripping fuel,plus make sure the float arm is level with the carb body when held upside down,could need adjusting??. After you clean it up use Stabil Marine fuel preservative OR StarTron. Will keep the fuel fresh up to two years and absorbs water better than regular red Stabil or any thing else I've found so far.Plus check the air filter and air box for any cracks. Plus fuel lines can start to disintegrate internally,clogging up needle and seats,jets,etc over a period of time. Just a bunch of things to check out. Hope this helps. Keep us updated. OPT

 

I pulled the carb, cleaned it and didn't see anything in it. There is plenty of flow from the fuel tank. The fuel filter looks great. It seems like the lack of power comes after the quad is warmed up and I've been riding for maybe 20 mins. I'm going to check the fuel selector ****. Maybe there's some junk in there. The fuel is in good condition. I use the quad a lot and cycle a lot of gas thru it so I don't think fuel quality is an issue.

 

Ok, now check compression while it's cold,then after about 20 minutes after running recheck it again! If compression is considerably lower (100 psi or lower), or even shows close to this when cold,then could be time for a new top end. I had this happen numerous times on two strokes when they get hot,cylinder expands and piston rings start to loose seal against cylinder walls dropping compression and either start running bad or dieing.
May or may not be your problem,but a good compression check could eliminate this as the problem. Plus check that the 3 way fuel valve is not stopping up or the selector **** isn't turning as you are driving it ,shutting down fuel flow.Plus you may need to check out the tank filters for any trash build up. Have had some run good on reserve, run bad on the on position,or vice versa. Had this happen on some of the older models. OPT

 

OPT, I just ran the quad. When it was warm the compression checked to about 110 PSI. When it was cold it was around 115. I'm going to pull the carb again and pull the jet out and see what happens. You mentioned the "tank Filters". Is this the regular fuel filter or are there filters in the tank? There is good flow when I let the fuel run both in main and aux on the fuel selector.

 

If fuel flow is good on both the main and reserve setting then the lines are ok from the tank.(there are built in filter screens on the outlet fittings in the tank) Sounds like you have it narrowed down to the carb,but compression is kinda on the low side and may need attention later. Keep us updated. OPT