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Fuel Screw Help
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Posted by: RemedyX

I 've purchased a used '01 250EX for my newphew, cleaned the carb and followed the performance FAQ's. I now have a slight poping when off the throttle. Will turning the fuel screw out solve this or am I heading in the wrong direction?

I have already searched thru many posts about the fuel screw. But, I need to know if turning the screw in reduces the amount of fuel in the mixture?

Posted by: Honda10

Ture the screw in, but there has always been a slight popping on 250s from the factory.

Posted by: RemedyX

Thanks, Honda10. I may just leave it well enough alone... It runs well other than that.

Posted by: Honda10

no problem if you ever decide to add an exhust or anything then you might want to turn the screw out a couple turns or just get the next pilot jet up.

Posted by: BR16250

check the spark plug buddy =] sounds like its time for a new 1

Posted by: tedwilley

Your idle mixture is lean, turn the screw OUT.
Read this for the explanation:
http://www.exriders.com/vbb/showthr...ight=fuel+screw

Posted by: dirtdawg

i'm having the same problem. i keep adjusting the fuel screw but i can't get rid of my backfire, and its running very hot! i'm running an fmf powercore 4 with a 110 main jet, stock filter, and airbox lid off. the plug is black at the moment, so it seems like somethin's up. do i need a new plug too? let me know.

Posted by: RemedyX

The plug is new, so I may turn the fuel screw out a wee bit.
Maybe 1/8 to 1/4 turn and see what happens. If it gets worse I'll put it back to where it was. It really runs well as it is.

Thanks for all the help gentlemen..

Posted by: dirtdawg

i have been turning it out, not in. so am i making it worse or better? does more turns out = less fuel, or does more turns out = more fuel? maybe i'm doing it wrong. idk.

Posted by: tedwilley

Read this:
http://www.exriders.com/vbb/showthr...ight=fuel+screw

I would suggest a new plug (and a spare) while you make your adjustments. You may be slightly rich with your setup and the stock filter, and your plug is fouled which will cause misfires.
If you are running lean through the rest of the throttle range the screw will not help. Your plug may have already been fouled.
Generally speaking, popping on decel is from too lean an idle mixture(if the jetting for the rest of the throttle range is right). That is what the screw adjustment is for.
If your running too lean, your engine will perform well, but run extremely hot and lead to a burned valve.
Best advice before jetting is buy two spark plugs, one to use while youexperiment with jetting, and one in case you foul the first one. Start over with a new plug and go from there.

Posted by: tedwilley

Out (counter clockwise) is more fuel, richer.
In (clockwise) is less fuel, leaner.
2-1/2 is where it is stock (approximately).
More than 3-1/2 turns out and you probably need one size larger pilot jet.
Less than 1-1/4 turns out and you need a smaller pilot jet.

Posted by: dirtdawg

i got a new plug but this time i got a #7 instead of a #8. i'm 4 turns out and i'm still backfiring! i don't know what to do. i can be 3 turns out and backfire as well. i have no idea now because it will idle perfect 4 turns out, but it still backfires. i put the airbox lid on to see if that would make a difference, but it didn't do anything. do you mean a needle jet when you say pilot jet? because there is no pilot jet but there is a pilot screw. it isn't running hot anymore though.

Posted by: tedwilley

There's two jets inside. The main jet in the middle and the pilot jet to the side of it. The needle and main jets operate from 1/4 to 3/4 and 3/4 to full open throttle respectivelt. The pilot and fuel screw adjustments are from idle to 1/4 throttle. Is it backfiring ONLY when you let off the throttle?

Posted by: dirtdawg

yes. it is only doing it when i let off. its running fine otherwise, but eventually this will screw up my valves. i don't want that at all.