450r carb tuning

[ahatcher21]

I have a 400ex with a stock bore. I have your usual slip on, airbox lid off w/k&n. Basic stuff. I put a 450r carb in there. I had the 48 pilot in there and had a bog, I had the A/F screw out 2.25 turns. I just put a 50 pilot in there, and it just revs like a son of a gun. I can't bring down the idle. As I'm turning the A/F screw out, is it giving the motor more fuel or more air the more I turn it out?

Any help with this would be great, I've been at this about 2 weeks now and haven't even had it out of the garage to see if the 170 dynojet main is correct.

[GPracer2500]

It's a fuel screw on that carb. Turning it out richens, turning it in leans.

Here's a repost of a guide to tuning the pilot circuit. I wrote it in reference to stock 400EX carbs but the method applies to any carb with a fuel screw. Maybe it will help.

Perhaps the best way to find the proper setting for the pilot screw (aka fuel screw) is the following. This method can also indicate if your pilot jet is too big or too small.

1) Warm up the engine to full operating temp.

2) Turn up your idle a few hundred RPM (basically you want a fast idle). This will make it easier to hear small changes in RPM. Watch for overheating--pointing a big shop fan at your engine will help it from getting too hot during the fast idling. The whole procedure shouldn't take too long though.

3) Turn the fuel screw IN until the idle just starts to drop and miss. If your pilot jet size is even close, then the quad should die before the fuel screw bottoms out. Each time you change the setting a 1/4 to 1/2 turn or so wait a 5 or 10 seconds to give the idle a chance to adjust.

4) Then begin turning the fuel screw OUT. The idle should peak and become smooth. Keep going and look for the idle to begin to drop/miss again.

The goal is to find the setting that provides the highest and smoothest idle. If it's unclear exactly were that point is then set to the midpoint between step #3 and step #4. For example, if the idle starts to drop at 1 turn out and starts to drop at 2 1/2 turns out then 1 3/4 of a turn out should be the correct setting.

If the peak/smoothest RPM is reached somewhere between 1-3 turns then your pilot jet is correct (the 1-3 turns applies to most carb types). If you end up less than 1 turn out then your pilot jet is too big and you need a smaller one. If you end up more than three turns out or the fuel screw seems to make little difference as you continue turning it out than you need to go up (bigger) on your pilot jet.

Typical fuel screw settings are in the 1 1/2 to 2 1/2 range.

It is quite difficult to adjust the fuel screw on a stock 400EX carb while the bike is running without a 90 degree screwdriver. I bit the bullet and bought this one from MotionPro. It works well but I'm sure there are others available.

http://www.motionpro.com/images/groups/144.jpg

[55belair]

:D one word edelbrock :D