i have a 400ex and the owners manual says it jetted lean for emissions. my bike is completely stock. how can i adjust the carb to fix this lean condition? do i adjust the skrew on the bottom of the carb, change the main jet or pilot, or move the clip? any help would be greatly appreciated

 

Remember,
You can loose power by doing this to. I have been trying to jet my carb, and have found that to be true. Keep in mind, more fuel doesn't mean more power. Remember, if you pour enough gas over a match, it will put the flame out. You burn fumes not liquid. Same as your ATV, more fuel CAN keep the spark low.

Rev. the ATV, if it sputters, to much fuel. Lean out the bottom end (keep it stock) fatten up the top end. The previous post was right, go only up one number on the main jet from stock. If your going to do this, also, change the air filter from stock to performance too.

Main jet starts to work after 1/8 throttle all the way to full throttle. Slow jet (pilot jet) starts working from idle to 1/4 throttle. If you like to cruise around, leave your slow jet alone on your ATV. If you drive hard (wot)change your main jet then. If you drive hard both throttle positions all the time change both then.

Ron

 

do you think it would be ok if i would just drill a hole or two in my air box lid instead of buying a high flow filter? the money situation is a little tight right now. thanks

 

To be honest, thats what I did. I drilled 1/4" holes every 1/2" apart.

 

thanks for the help. i think i will drill holes in my box too. by the way does anyone know the stock pilot jet size? i know the main jet is a 148 and i already have the one size up but i need to get the next size on the pilot.

 

i figured out the pilot jet is a 38. with me modding my air box lid will i only need to go up one size on the pilot and main jet? if so i will get a #40 pilot jet and i already have a 150 mainjet. i did not know if i would need bigger with that modded lid or not. i guess i will leave the clip in the stock(i think third) position unless otherwise told differently. also should i leave the pilot skrew about 2 1/2 turns out? thanks once again

 

My kids ride mine, so I did it reverse than your's.
My stock was #148 on the main and #50 on the piolet (slow). I left my needle on the 3rd notch too. As for drilling the hole, you can hear the exhaust coming in better as for changing the mixture (lean or rich) I didn't notice anything.
The best way to tell if you did it right is to CHECK THE PLUG (put a new plug in) and ride it like you always do (for about 15-30 min.) then pull it out and check it. Then do a (WOT) plug chop (to check for top end being to lean). Get it up to 4 or even 5th gear WOT (wide open throttle) for a few minutes, then pull the clutch in and shut it down, then pull the plug. Post your findings for both readings or email me directly.

Good luck, post your findings
*remember, I have a 250r ATC, not a quad.

 

i will post my readings. it may be a few days because i do not have the pilot jet yet. i am not sure how quick i can get to the shop. thanks for the support