carb questions for a yfz400

[litenup]

bought it used. guy had no clue what he was doing. im only slightly more informed as i have read a few post here on the subject. im getting to much fuel, its poping the gas as it ignites coming out the muffler, inside the bottom of the carb are the flat head screws(jets?) with holes in the middle of them. ones in a plastic cup, other is open, last is in a steel tube. cup says 124, open is 60, and tube doesnt have anything. wich do i turn to lean out the fuel. seconed is, are these the stock jets if im correct as to what they are? next, im guessing the needles are on the other side of the screws, how do i get to them to adjust the clip if i need to adjust that as well?

[GPracer2500]

This might help:

http://www.bikebandit.com/partsbandit/assets/schematics/Yamaha/YA5837_14.gif

#18 is the main jet--controls fueling from about 3/4 to full throttle.

#20 is the starter jet--part of the enrichner (choke) circuit. You shouldn't need to change that.

#21 is the pilot jet
#23 is the fuel screw

#21 and #23 work together (along with #22--but you don't have to worry about that one) to form the pilot circuit. This circuit controls the fuel metering from off idle to about 1/4 throttle. Well, the AP comes into play here too, but first things first. Turning the fuel screw out richens the circuit, turning it in leans the circuit. Don't torque down on that screw--all settings are measured from lightly seated. The stock setting is probably about 1 3/4 turns out. Don't go more than 3 or 3 1/2 turns out (any more than that and the fuel screw has reached it's maximum adjustment range and the pilot jet needs to be changed).

#14 is the jet needle. It dominates the fuel metering from about 1/4 to 3/4 throttle. It is accessed by removing the top cap of the carb. Moving the clip down raises the needle up resulting in a richer mixture. Moving the clip up leans the mixture.

Factory Keihin jets will have a stylized "K" stamped on them next to the numbers.


The Keihin FCR (that's the carb model) found on the 98/99 YZ400F was practially the first production motorcycle to ever come equiped with an FCR. MANY revisions have been made to the FCR since then. I've worked on one YZ400F FCR and it was a royal pain to tune. I'm not sure how much of that was due to the carb just being worn out--we never did get it just right. Basically, I'm saying you may have picked a real humdinger of a tuning challenge if you're not experienced with carburetors.

[litenup]

that is exactly what i needed to know. with that info i can take and adjust it as needed. dont think the jets are stock then. dont remember a "k" on em. ill have to check again. hopefuly i dont have to replace anything in the carb as curently my funds for repairs have vanished.
not experienced with carbs but im quick learning and undterstand mechanics and concepts very well. if anyone can get something running without knowing anything about it, its me. ty again

[bradley300]

places like carb parts warehouse should have all the jets you will ever need for that carb, and i think all of thm are under 5 bucks a piece