air box puzzler

I'd think you'd need to make the jetting a bit richer to compensate.
Turn the air screw in 1/2 - 1 turn. If that don't fix it then change the pilot jet to one size bigger (higher #).
You'll also have to change needle position (higher) and change the main jet to also be richer.

Hmmm, it sounds as though your airbox lid is providing some choke to the carb by reducing some airflow. This would be a symptom of very lean jetting in the pilot circuit. Before you start changing too many things at once do a little test. Get the bike started and warm it up. After the bike is warm engage the choke. If the rpm’s rise and the throttle response improves you definitely have a lean pilot circuit. You can adjust this with the air screw. If the airscrew range goes beyond 1 to 2 turns you’ll need to consider a richer jet in the pilot circuit.

What is your current carb set up?

Try this: Start the bike first, then while it's running remove the air cover. If it immediately quits, you probably have an electrical problem [loose wire or connection] from "tweaking" the wiring harness. If the engine speeds up, then it's too lean --rejet accordingly.

I'd suggest the above tests before you start pulling things apart. Lets fix one problem at a time. We can look at the jetting at anytime.

FYI, the jets can be accessed by rotating the carb and removing the float bowl (make sure the fuel has been shut off!). There are two jets, the main is in the center and the pilot is off to the side. The numbers are stamped right into them.

You will have to remove the bowl from the carb to get at the pilot, which means you will have to remove the carb from the bike.
You can actually get to the main jet via the large plug/drain on the bottom of the float bowl without removeing the carb.

It sounds like you need to pay a visit here http://justkdx.dirtrider.net. Check out the tech tips. There is a wealth of info in there on KDX's.

Have fun!

Read what RV6 said. Fix one thing at a time. The bike should not fail to start with the simple removal of the airbox lid. It's probably something other than jetting. Robcolo already said what to do about that.

You don't have to take the carb off to change any jet in it. The TV (throttle valve or 'slide') and thus the needle and clip positioning can be accessed from the top of the carb with it still in the boots...just loosen the boot clamps to rotate the carb for access.

Likewise, the fuel bowl comes off with the carb tilted in the boots, too. It helps a whole lot to replace the phillips screws on the fuel bowl with allen heads. Get a ball-end driver for your fender bag. That will make fuel bowl removal a snap.

Put some never-seize on the fuel bowl threads to save yourself some hassle in the future.

The pilot jet is not visible. It is screwed into a cavity (recessed hole?) that is directly in front of (downdraft side) the main jet. Access it with a small common tipped screwdriver.

Keep in mind when changing these jets that they are brass. That makes them soft! It doesn't take much twist to snap a main jet into two pieces.

Not that removing the carb is a big thing. You can take the whole thing out in less than a minute. That makes things somewhat easier.

Make sure the bike isn't covered in muck when you do any carb work.

You find any experts around, let us know. We'll do what we can to run 'em off! (ex=has been spert=drip under pressure)

Any other issue notwithstanding, removing the airbox lid will reduce the pressure differential that the carb runs on which will effectively result in a more lean A/F (air/fuel) mixture.

You mention not knowing what your current jetset is. There is the possibility in that case that less fuel could damage your motorcycle. The chance of that is slim, cuz it's unlikely your bike is jetted right on now.

Placing the CDI unit any place secure is fine. Don't stretch/kink/stress the wiring. Don't let it flop around. A tie-wrap will work. Using an existing threaded hole or making a new one will work, too.

It's not just the pilot that's effected in this case. Removing the lid will effectively lean every circuit. There is no replacement for the individual rider jetting his personal bike.


I hope you post the resolution to the 'bike won't run' that started this thread.