I have a 2000 400ex and just put a K&N Power Kit and MegaMax Silencer. Put a 40 Honda Pilot jet wit the 50 K&N main jet. It still has a little hicup when I blurp the gas. The mixture screw is 3.5 turns out. I am starting to wonder if I should just go back to stock jetting or what. Do you think if I mess with the mixture screw or what? What is the stock mixture screw setting? What does turning it clockwise do? Just wondering. Maybe one day I will get it running right.

 

I hope you get help from a knowledgeable poster, Mulder99; if your 400 has a Keihin CV carburetor, turning the mixture screw clockwise makes the mixture more fuel-lean (because the mixture screw is on the engine-side of the carburetor; if it were on the airbox side, the opposite would be true). As to stock screw starting position, the tuner's rule-of-thumb for an unknown carb is two turns out from the bottom (close it softly, you don't want to booger the seat), adjust from there. Good luck!

Tree Farmer

 

I would have to agree that 3.5 turns out seems a bit much(rich)...I would take Tree Farmers advice and start around 2 turns out and see what happens.... Why did you mess with the pilot..Just curious? With those mods...the stock pilot should have been just fine....maybe 2 sizes larger on the main....I Also have a 400ex along with my Banshee...the Banshee gets all the mods...and the 400 stays stock for My fiance'... Soon enough I guess she will want a pipe and such on it....But for her type of riding..it works just fine.

 

Reason I put the bigger pilot jet was because repost said that controls the first part of throttle response. It used to smoke real bad and not harldy idle before. That was with the 170 main jet also(as informed to do so persay K&N instructions). Do you think that (mixture screw adjustment) would cause it to studder on quick acceleration? I mean it is nothing like stock. Well, hope you guys hang in there with me cause I sure do want to work these problems out. Thanks.

 

When you say "Studder".... does it go away when you are in the meat of the power band (high revs)...Or seem to studder all the time?

What gap are you running on your plug?

I would also say to change the plug after a drastic change with the air screw...the studdering could be the plug that was running rich.
what color is your plug?

 

Mulder99, Normally I would not suggest this, but since you asked this question, I will: "I am starting to wonder if I should just go back to stock jetting or what".
I'd say go back to you stock settings on all mixture/air or whatever screws. If you have done anything with the jet needle return that to 3rd position. Replace the stock pilot jet. Now, you are back to stock in every way, right?
If the only airflow modification is the silencer, no pipe or no K&N filter, the chances are you need no more than one size fatter main jet. Since K&N uses propriatary numbers for their jets, you'd have no idea what their next size up is, so my advice to you is to contact your dealer & buy a $3 main jet one size fatter than the stock.Stick it in & test ride in the 3/4 to full throttle range for a mile. Cut the engine right there & read the plug. If it's tan or brown your main rejetting in done! Now you can address the other ranges & deal with them if necessary. Regardless of what certain manufacturers tell you, the cardinal rule in adjusting any thing is to adjust only one thing at a time, then go to the next if necessary. By now you have an idea of my opinion of jet kits. They're solutions to some problems that don't exist!

 

on Keihen FCR carbs the idle mixture screw is on the engine side of the carb slide, and you adjust the screw out(counterclockwise) to richen the mixture. on CR,PWK,PJ and PE carbs the idle mixture screw is on the air filter side of the carb slide, and you adjust the screw in(clockwise) to richen the mixture.
the idle mix screw will be the brass straught slot screw.
the idle speed screw will be the plastic screw with a spring behind it and will be located in line with the slide.
It sounds like to me you have a rich condition at idle, a lean condition will have a higher idle and be very responsive.

 

Here is tje latest and greatest. Ran like crap till I readjusted the mixture screw to 2 turns out. Now running with the K&N 150 main and one size bigger Honda pilot. Drilled about 15 .25 inch holes in air lid.
It is awesome!! May have lost some top end but good lord, bottom end is sweet! It's like a totally different bike. I am very happy with it.

Thanks to everybody that gave inputs and suggestions.