Maintenance & Technical > KX500 Original

KX 500 Flat on Mid and top end

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lsampson:
Hello All,

New to the site, so be gentle :) I have a 1991 KX 500, all stock, that I'm putting a top end into. I have several questions.

1. When I rode it prior to tearing it down, it didn't have much spunk on mid-top end. I checked for exhaust valve operation, and they were functioning. I also cleaned the jets and they were clean. I cleaned the whole carb thorally. The bike was from my uncle, and it should be jetted right, but it is running a 160 main, 45 pilot, with the needle clip set 2nd from top. The elevation I ride is appx. 6000'. I found a jetting chart, and it looks close. The plug is a little on the lean side, but not bad. During teardown of the top end, I  inspected the power valves, and they WERE gummy, but still functioning. Anything else I can look at since I'm this far that will solve my flat mid-top end performance? It starts easily, but during deceleration it kind of "chugs" to a stop. Idle is ok.


2. I have read the outline of power valve re-installation, but am a bit confused. I have the powervalve with the notched top pin on the right side (the counter gear side), and aligned it with the rack, aligning the dots. When I fully close the rack (pushed in) the valves expose some of the exhaust valves, probably half of the outer exhaust port.. Only when the rack is pulled out some do the exhaust valves fully close. Is this to compensate for idle RPM, thus pulling the rack out and closing the valves? I have a sneaking suspicion that this is the reason for the ball bearing mod?

Thanks a bunch for the help.

bilger69:
Maybe stator position. I found this problem when I messed with advancing the timing.

bilger69:
Actually it is a better chance it could be  the kips arm.    Here's an explanation of a problem I had with it a while back.                                                http://www.kxriders.com/forums/index.php/topic,9425.0.html

lsampson:
Thanks Bilger. I'll look into that. Have you torn into the Exhaust valves at all? I took them completely out and accidentally mixed up the right and left valve. There is only one way they can go in and still function correct? The Kawasaki book mentions a right and left for the 125 and 250, but not the 500. The reason I ask is the "barrel" valves seems too far closed with the rack pushed all the way in. At rest, you can see around the valve and into the cylinder exhaust port (one of them anyways) then when you pull on the rack the valve closes the ports, then full open it opens up both ports.

motopunk:
the left and right exhaust valve of the kips-system had to be fully closed at low rpm. check out, that all valves are fully open at high rpm! if it installed in wrong position it cant work properly.

stator position is in stock the middle of the 3 marks on it.
i think that the old piston already had too low compression. check the motor performance after rebuild again. when piston and exhaust valve work in right order, you can only continue with the ignition and carburetor adjusting.

at last, go with your ignition system to a kx dealer and let it measure whether everything in it works proper.

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