carb settings

[ridinrednIL]

I'm using a 150 main, 32 pilot, and clip on third from the top on the needle jet. Temp here is about 60-70 degrees. I have a slip on and no lid on the air box. My problem is this: It starts and idles great. Top end seems to be o.k also, but it seems to have a slight lull off idle. If i set at idle and give it gas it has kind of a flat spot. honestly not sure what mixture screw is set at.

[jbm0121]

i have the same problem no one replied to my thread...if they do ill let you know

[hornetgod13]

You need to fine tune the fuel screw. I think you meant 42K Pilot right? You type 32.
I had a similar problem and adjusted my fuel screw in or out a half turn and raised the idle slightly and it got much better but, what really cured it was, installing a Curtis Sparks Advance Timing Key. It makes for quicker, snappier throttle responses and faster acceleration.
See the following article for more information and how to install.
http://www.atvriders.com/articles/timingkey400ex.html

[GPracer2500]

The issue is the carb's accelerator pump not keeping up. When you wack the throttle open at low rpm (especially right off idle) the slide opens and the engine takes a big gulp of air. It takes a second for the carb to catch up and start delivering fuel thru the needle and main circuits. This is a fundamental limitation in the way carbs work.

But that's why there is an AP. It's there to mechanically squirt a shot of raw fuel straight into the engine when the throttle is quickly opened. It's mechanical so it happens right away. The other carb circuits work off differential air pressure so their response is not instantanious.

The problem is the 400ex carb's AP doesn't have any built in tuning features (unlike an FCR). It squirts what it squirts and there's not much you can do to change it. So, when you run with no airbox lid and other mods you can get this lean bog. All you can really do is tune (and ride) around it the best you can.

Like hornetgod13 mentioned, turning up the idle a little and fine tuning the pilot circuit can make a difference. I haven't heard of extra ignition advance providing relief but maybe it does.

With my old 400 I found that the lean bog only really occured if I was actually trying to make it happen. Under normal riding I never noticed. Or maybe I just learned to ride around it without having to think about it.

[drillteamleader]

there is one thing yoiu can do to the ap. If you bend the arm that pushes the plunger farther away from its pivot point it will move the plunger farther. its not much, but it cured theproblem for me.