powerband and powervalve problems???

[jdager]

Hi all,
I have a new kx125 that I bought a couple of days ago. I rebuilt the whole topend with piston, rings, gaskets, the works, hoping that would take care of my problem, but no such luck... it starts and idles fine, and runs fine in lower rpms, but after 1/3 to 1/2 rpms, the bike falls flat on its face, and will not go anywhere, just like its stuck. the piston had a funny carbon buildup pattern on the top, and I included a picture of it. there is also a black dot on either side of midline on the front side of the piston, towards exhaust. I am thinking maybe it has something to do with the KIPS powervalve, but I have no idea how to check it, how it should function, or what it should look like? any help would be much appreciated.
thanks,
Jim Dager
I hope the link works, the bottom of the picture, where the triangle of carbon is widest against the edge of the piston, is the front, towards the exhaust.
http://i394.photobucket.com/albums/pp23/jimdager/piston2.jpg

 

[schmanman]

hmmmmm...

have you experimented with the jetting at all?

 

[jdager]

not yet, I put it to fmf specs. I just finished cleaning the powervalve, and it made a lot of improvement, but it still feels like it falls flat on its face???

 

[_JOE_]

Go get a service manual.

When you had the cylinder off did you try and operate the power valve manually? The valve should be partially blocking the exhuast port until around the midrange when it opens up. This changes the flow through the engine to provide better low end power. Never seen the KIPS system, but suzukis use a centrifugal sytem in the bottom end that pushes a rod running up into the cylinder. The slide is attached to a linkage system that is controlled by that rod. After a while oil builds up in the system and gums it up. This build-up will eventually cause the valve to stick. Seems to be more commonly stuck closed.

Check the main jet to make sure it's not plugged.

 

[_JOE_]

Dang, I missed your last post. :bang:

Did it do this prior to jetting to FMF specs?

 

[whenfoxforks-ruled]

Do you see the wear mark from the exhaust bridge? Did you do a leak down test? A 97? How bad does it smoke? Chances are really good that the right crank seal is gone. Them black rubber seals can get hard over the years, ALL the black rubber on your bike as a matter of fact. You really need a service manual, and replace all the engine seals. If not the crank and trans bearings also. Then you should have a solid engine. Take your intake and airbox boots and bend them slightly, look for cracks. When they fail, it will suck debris and ruin the engine. Watch the clamps also, if they screw in all the way closed, they are stretched and shot. Lastly, check the airbox seal, reeds and change the silencer packing. And the power valve, leave the cover off and start it. Does it open after half throttle?

 

[cookedm]

sounds like when you start getting up enough speed it gets too much gas and floods out does the plug foul out?

 

[XRpredator]

ugh, two strokes are such a maintenance headache . . .


;)

 

[Rich Rohrich]

ugh, two strokes are such a maintenance headache . . .

... much like you Pred. ;)

 

[YZThumper]

Did you disassemble the powervalve when you rebuilt the top end? A lot of people don't, but I personally belive it's as important to do as the piston & rings themselves.

I had a 2001 KX250 and took apart the KIPS valve when doing a top end a few years back. The gears on some of the valve rods in the KIPS system tend to get deformed and in my case, some of the teeth were broken off. This may cause the powervalve to not open properly or not open at all.

It sounds like your problem may be powervalve related, given that it falls flat at the top of the RPM range.

Did you also check the reeds when you had it apart?

 

[jdager]

checked the reeds, tiny chip out of the corner of one, but doesnt seem to be affecting them closing, I will replace them anyway. I didnt take apart the valve, but cleaned it up good. I want to take it apart and clean it, but when I tried, I could not for the life of me figure out how to get it out of the jug. anybody have any tips, or pictures of how it comes apart, the service manual wasnt much help.

 

[jdager]

doesnt seem to foul plugs, but I havent run it enough to really know. doesnt hardly smoke at all, seems to run hot. I will check the operation of the valve visually tonight. when I had the cylinder off, but valve seemed to move freely by hand. the rod going to the engine seems to have a lot of tension on it, should it? if I have the engine apart, I will probably do an entire bottom end job on it. what is involved with that, and what parts should I replace? any good reference for that? what kind of price for parts, and parts and labor should I expect?
thanks for the help,
Jim

 

[RM85rider123]

ugh, two strokes are such a maintenance headache . . .


;)

Your just jealous. :yikes: