KDXRIDER.NET

Hi guys,

I just bought a bucket of parts and put it all together and a 1990 KDX 200 came out at the end of it. It's starting on the first kick and running great up until it should break into the power band. I was unfamiliar with power valves when I assembled the top end and just put everything together in a manner that seemed to fit. When I encountered the issue I read into power valves a bit and popped off the KIPS cover on the left side of the cylinder. The little rod is moving out as the RPM's rise so I assume everything on the Right side of the Cylinder is functioning properly. Could the issue still be a power valve related issue or am I looking at maybe and gunked up carb jet or reed cage problem. Also not too familiar with reed cages or how to check for problems there.

Any tips or further information would be much, much appreciated.

thanks

The left, right and center valves need to be lined up. There are small timing dots on top of the valve gear teeth. Your centrifugal governor is operating the shaft, which engages at 6000rpm, so that's good. The center valve should be open when the rod is pulled all the way out too. That's easy to tell by he cup in the valve matching with the cup in cylinder exhaust porting.

Get the service manual, is the cheapest and safer way to do the things right the first time.

+1 on the manual.
then check my sig for how to for newb.

check for frayed reeds at the corners.
try leaner main jet.
check cylinder compression. if bad check for tight head nuts and check ring end gap.
a malfunctioning KIPS will reduce the power at top rpm but not cause it to run like a dog.

Not a lot of info to go on....what issues with powerband? flat, bogging, burbling, tailing off, etc? what throttle settings-off idle, 1/4, 1/2 etc? Reeds should lay flat on the cage with no gaps, no cracks, tearing, frayed corners, etc. ensure mechanical soundness of intake/exhaust track, clan carb (really clean it, disassemble it and pull the jets, write down the numbers, clean it well but don't soak it) and run through the jetting guide to see where you sit

Isn't the manual a little off about how to install the valves, or is that just for the newer E series bikes? I know that the 89 manuals instructions where quite off on how to install the valves, but my bike is a 94, with the slightly different valve design.

Yea in 1991/1992 they started making them without a rounded-out section in the center valve, so they couldn't be pulled back and positioned with the rod installed. No idea what process the guys use with the newer ones

http://www.kdxrider.net/forums/viewtopi ... 0&start=20

Bufftester:

The powerband is non existant. The bike starts, idles and accelerates very well all the way through the mid range but just stops building RPMs and hangs where its at when it should move into the power band. Plenty of throttle left when this happens. RPMS remain static even when I roll all way the back. I cleaned the carb today, pulled the reed cage and two of the reeds where not flat against the cage. I flipped them over and one still remains raised slightly. I'm going to replace that tomorrow (parts store willing) and see what difference that makes.

consider bad crank seals

Check the valves first. With the RH KIPS cover removed does the rod move when you rev the engine? If yes, Pull the exhaust and extend the KIPS rod by hand while watching through the exhaust port into the cylinder. The valves should all three be open with the rod extended, and closed when the rod is seated. If no, remove the RH cover and look for a broken pin at the bottom of the actuator rod.

The culprit was indeed the reeds. Got the new ones in today, put it all back together and it zoomed right into the power band. Thanks for the help guys.