KDXRIDER.NET

Short version, just bought a 2000 KDX220R, power delivery is ODD at best, super soggy low end-mid, VIOLENT power band hits at the very top with no RPM after the power band hits. Previous owner recently had the engine rebuilt, appears the sub valves of the KIPS are operating opposite of what they should, they are open when they are supposed to be closed and close when they are supposed to be open, (Sub valves are open w/engine off/idle, the sub valves then close as RPMs increase to full closed at high RPM), main KIPS valve is fine so no issue there. Pretty sure the Sub valves are supposed to be closed at idle and then open as engine revs up, right? If that is right, how could those sub valves get installed/connected to operate in reverse of their design? Should be a simple fix right, just swapping the rotation/parts side to side?...

Long version, few weeks back finally bought a KDX, (been wanting one for years, this one popped up for a great deal, snagged it).
This 2000 KDX 220R is essentially stock, pipe, carb, etc, though pretty sure has an anomaly, put approx 50 miles on it so far, bottom end power is VERY soft, (softer than my XR200), power band is a VIOLENT hit at top of RPM band, then maybe 500 RPM more above that and it falls flat on its face.
I verified the KIPS shaft rotates as engine revs via watching shaft operation under the left side slotted screw cover and it does move as seen on youtube videos as engine revs... As I understand, shaft rotation alone does not guarantee actual KIPS operation...
Previous owner said piston grenaded approx 20 hours back, he had the engine rebuilt back to stock, had the jug sleeved, (after pulling the head looks like the sleeve job was done well, no porting perse, only cutter marks are from blending the sleeve to the ports and done very well, nothing more).

Today I pulled the head and carb to send to RB for his magic, after removing the head I manually operated the KIPS via the shaft under the left side slotted screw cover.
Main valve is partially blocking the roof of the exhaust port down as it should, rotating the KIPS shaft the main KIPS valve pulls back out of the way as it should, nice and smooth, returns back to covering the upper portion of the exhaust as the shaft is released returning back to idle/engine off condition, no issue.
Sub valves... They are WIDE OPEN at rest, engine off/idle position. As I rotate the KIPS shaft the main valve retracts out of the way as it should and my the sub valves then rotate to the closed position, i.e. at idle and low RPM the sub valves are open, as the RPM rises the sub valves then close. This seems backwards to me, can someone confirm my suspicion of this being the issue or?...,
Looked through my factory service manual, didn't see mention of what posstion the valves are supposed to be in at what points of RPM range, idle, etc.

At low rpm your kips should be closed. The claw all the way to the right.

Update...
Stopped by RB Design's shop and picked up my carb and cylinder head, FIRST rate craftsmanship and customer service, it doesn't get much better. Thank you Ron.

After some more digging and talking with Ron I lifted the sub valves up to remove the bushings, with a flashlight peaked down in to very sub valve timing mark alignment, BINGO! Sub valves were timed approx 90 degrees out. Was able to lift the sub valves enough to disengage sub valves from the sub valve shafts and clock the sub valves correctly, dropped them back into engagement, PERFECT! No the sub valves are closed at idle/engine off and open up as the roof port flap retracts as it should.
Now just awaiting for the head gasket and Boyesen 607 reeds to arrive, assemble, dial in and enjoy.




Disclaimer, any other newbs reading this, do NOT rotate/actuate your KIPS manually unless properly disengaged to avoid breaking the pawl. As I understand it, I got lucky, VERY lucky as how I manually actuated the KIPS breaks the pawl every time.

Update;
Gaskets and Boyesen 607 reeds arrived today, new NGK BR8EG spark bolt, assembled everything, fired right up, adjusted idle speed, let it warm up.....

AH MAH GAWDD! Throttle response is RIGHT NOW, instant, no-load it revs so QUICK! cruising around the pasture for a test run, so much more power now, no real perceptible "hit" just a smooth steady build of torque a the RPMS' rise form off idle, no flat spots, just easy to manage, predictable, "refined" power delivery form idle all the way up, in third gear the front wheel lifts slightly as the RPMs rise, so FUNNN!. In first or 4th, no hiccups, just wonderful crisp refined power delivery. Couldn't be happier. Hats off to Ron Black for his work and greatly appreciate him taking the time to help me sort out the KIPS power valve issue.

Update... Put 150 miles on it now, mostly single track at 4800 ft in central Oregon, ZOMG! This bike is AWESOME! As a professional engine builder/machinist/tuner in the sports car world I tend to be a bit hyper sensitive to drivability, throttle response, power delivery... Etc. I have yet to find fault or flaw in how this bike runs, responds, and delivers its torque, It is very clear that Ron Black has a firm grasp on what is required to refine the KDX carb and cylinder head, refining this 2 stroke to such an amazing level. At this point, there are NO more mods planned for the power plant, time to refine the chassis to match the powerplant.

Hiwerver wrote:There are certain things that I want and need to know.

Yeah, go ahead.