Alright guys, don't hang me, instead just humor me! I would post this on a site for 2-stokes if there was one this caliber. I know most of you have had 2-strokes at one time so I would appreciate a little help.

I am trying to sell my 2001 KX 250 but before I do, I want to remedy a nagging carb (?) issue. I changed my jetting the first day I bought the bike and ever since then, it hasn't been the same. The problem: Anytime I rev the bike and let off (either in neutral or clutch in) it takes a long time before the RPM settles down again. Also, when riding into a corner and letting off on the gas as I decelarate, the bike acts kinda like it is running out of gas (or really lean).

Since then, I have changed every jet/ needle in the carb, returned back to stock everything, and adjusted idles and air screws, but it still has the same issue. I even sprayed WD-40 around the head while the bike was running to see if any air leaks but nothing.

Any thoughts from any of you glad you have a thumper now?

PS: I do have a 2001 and 2002 YZ250F - so can I stay?

Mike

You have the classic airleak. Check the left side crank seal behind the magneto. Check the intake manifold both where it bolts to the cylinder and where the carb attaches. You could have a leak on the primary side of the crank, buy that would be noticeabel with lots of smoke from gear oil being burned. Check that the choke/airscrew/TPS/carb top are all attached correctly.

Odd that it started with a rejet. Wisdom says to look at the last that was changed, thus the carb. Maybe get some one else to double check your carb assembly. We tend to over look our own mistakes, multiple times.

let us know what you find, eh?

VT,

Thanks for the reply! What is an effective way to test the left crank seal? And in checking the intake mainfold, would I use the same approach with the WD-40?

In terms of the changes, I have had someone else inspect the exterior or the carb/boot/manifold, but I will try to get someone to check the inside.

Also, I will be out of town in a week for about 5 weeks so I won't be able to get to it until I get back but I will post back with results.

Mike

Check the crank seal the same way as the manifold. spray something volatile (ether, wd-40, ...) and if the rpms go up temporarily, then that substance is getting into the engine through the leak. The left side crank seal is easy to replace (assuming you have access to a flywheel puller). Still I would concentrate on the carb and manifold if that is the only thing you messed with.

OH yeah, just thought of one more thing. Make sure the throttle cable in routed properly and is not binding anywhere. (usually under the tank or at the steering head)

Great, will do!

Two other things to check are the base gasket and the gasket/o-ring on top of the carburetor and if nothing shows up, you may need to pressure test the engine. A good shop should be able to do it for you. Also I believe the company Motion Pro may make a kit to test the engine for leaks.

First off... you need to make sure that it is indeed an air leak.

Have you done a jetting run (run it wide open, then pull in clutch and kill it, then check plug)? If not, make sure you do that before you dive into any other solutions. If the plug is white, you have an air leak. If it is dark or tan, unfortunately your problem is not an air leak... and can be very challenging to figure out.

If your plug is white... then check the things these guys have mentioned, ex: Head/base gaskets, carb/manifold gasket, crank seals.

But first, before you pull your hair out trying to fix the air leak, make certain it is in fact an air leak.