2000 xplorer 250 2stroke. out on the air/fuel screw=leaner, in on a/f screw=richer. correct? my machine is running best (highest idle) at 3 turns out on a/f screw. manual states 1 turn out. with that said, can someone confirm that i would need a SMALLER pilot jet? it seams strange to me because i bored over this machine last yr and everytime ive done an over bore on an engine, i needed a LARGER pilot after the bore job. any thoughts?

 

1 1/2 to 2 turns out on average. Just drop the clip on the slide needle one notch to richen up mid range and see if it helps first. If it doesn't help go the other way.Stock 40 pilot should be sufficient even on an over bore. Plus don't over look float level. With carb held sideways with float barely touching float needle,bottom of float should be around 0.51. (13mm) to carb base.

 

I think im in the middle poss (3rd slot) and ive tried the other positions with no improvement. there has also always been a slight stumble at 1/4 throttle where I would presume was about the end of the pilot circuit. it goes away after about 10-15 mins of good riding.

so can you confirm that out w/ fuel/air screw is leaner and in is richer?

 

Out on the fuel mixture is richer. out on an air mixture is leaner,,,,so is you screw after the bowl toward engine? thats an fuel mixture screw so out wouldbe richer. if screw is before bowl toward air filter then that wouldbe an air mixture screw so out would be leaner.

 

If you are turning out an no change in running then may try take carb down an clean real good an also check for air leaks in intake manifold,cracks,oring flat,clamps, mounting surface flat an not warped.I spray wd 40 around carb while running mounting and if engine loads up an going dead or runs better then air leak in that area. If runs the same then IMO carb could use an good cleaning,and adj float level like OPT mention to get the correct fuel level needed for idle.BUT I think the correct way to adj the pilot mixture[fuel mixture] is at normal operating temps bout 10 or 12 mins of running time to make sure engine is running off idle curcuit not starting curcuit,,alot of atvs have cold mixture to lean until normal temp before any adjustments are needed.

 

As papa said out on an air/fuel screw such as your 250 is leaning the mixture. Basically allowing more air,less fuel.IN shuts down the air allowing more fuel This screw is less critical than a fuel/air screw that's on most 4 stroke engines. This adjuster is closer to the front of the carb and way more sensitive on settings. Engine idle difference is less noticeable between 1 1/2 to 2 turns on this little piston port engine. The rest is up to the main jet, needle jet,jet needle and pilot jet. Change to a 45 pilot and try it. If it doesn't help,just install a new carb kit including the needle jet and jet needle. These could be worn causing mid range problems. This is a basic first generation engine that suffered with mid range hesitation/bog problems as all piston port engines did. They came alive in the next generation when reed valves were introduced such as in the early Honda 250 Elsinore dirt bikes.Little air cooled engines that could scream.

 

Shouldnt the pilot jet and screw controle idle speed in an ideal carb set up. As in the actual idle adjustment screw really shouldn't be holding the slide up? Follow me?

 

Not really.. The big knurled IDLE adjuster screw does what it's name says,just adjusts the slide higher or lower which also raises or lowers the engine idle also. The internal pilot jet(idle jet) allows the proper amount of fuel for idle,that is if you have the correct size jet. The AIR/Fuel screw just fine tunes the air to the fuel mixture from the pilot jet that is allowed through the carb venturi into the engine so you should have a steady,even engine idle without bogging,blubbering from too lean or too rich of a mixture when you blip the throttle.If you adjust this screw while it's running and find that it idles best with the fuel air screw almost CLOSED,then the pilot jet is too small. If it fine tunes around a base setting of 1 1/2 to 2 turns and takes the throttle ok,then the pilot jet is the correct size for this carb. Best I can explain it to you.
See if the junkman in his eloquence can explain this better for you on his video.Like they say, a picture is worth a thousand words!

 

most all carb should be 1 1/2 to 2 turns out, if ever thing is set right, float hight, needle is in correct, position on carb of a/f screw in front or in back of slide tells u what the screw is letting in, between slide and air box the screw lets in air, between slide and cyl. screw let fuel out of carb in to motor, if you screw is a fuel screw (between slide and cyl) and is at 3 turns out, u need more fuel/bigger slow jet, if its an air screw (between slide and air box) is 3 turns out u need smaller slow jet. u need to make sure the float is good and set correct and the needle is in wright, correct spacers and clip position.

hay OPT u look a lot younger that video

 

Nope,not me.. I would like to swap years with him though...