A "Low Power" problem solved - READ!

[ACGUY]

My neighbor recently picked up a 96 KDX 200 for a great price. It was in nice condition, but was a little low on power in my opinion, but I told him it probably needed a top end since the folks that owned it probably neglected it a bit. All it needed was a new air filter, some leaner jets, and the bolt to hold the filter in, so he replaced all. We also put a KX250 silencer on it, which added a little of that "factory 250 sound". He rode it a while, and we frequently compared his to my 97, which is ridden very little, and the power difference was night and day.
We both had some spare time this week, so I convincd him it was time for a top end job to fix this loss of power. I had to work late a couple of nights this week, so he and a buddy were going to perform the teardown, provided I was there to do the critical measurements, and put the motor back together.
So today while I was at work, he calls me and says they took off the pipe, and it was about 60% restricted around the lip of the exhaust pipe, and it was heavily plugged with carbon (about 1/4" thick). I told them to clean up the carboning, and flush out the pipe. They did, and then proceeded to remove the jug. With the Kips disconnected, the jug was removed. After rotating it 180 to view down into the cylinder, they noticed a rattling noise. They shook it a bit to duplicate the rattle, and the air filter bolt and washer/wing nut fell out of the reed cage onto the floor!! Apparently this bolt was laying in the reed cage, in the gas path, blocking airflow thru the motor, which in turn caused the heavy carbon buildup. Needless to say, the piston was covered on top, and the Kips was pretty chalky too. The rings measured .024 and .030(old), and new .012 each, so we are going to surface the cylinder walls, clean the kips, and slap her back together.
I will update in another post regarding the power gained from these teardown finding corrections. :thumb:

 

[gooby]

O....MY...GOD.the previous owner must b somethin.how does that happen lol.keep lookin no tellin what treasures u'll find.....rolls of money in the gas tank ;-0 .sounds like the bike is in good hands now tho.

 

[jpm200]

You might have to return the jetting to the original settings
I love previous owner neglect, gives you a better feel for the bike. If I didn't I would always buy new bikes.

 

[Jim Crenca]

One tip for cleaning expansion chambers is to use a few ball bearings and some automotive break fluid as a cleaner; cap the ends and shake it up. How are you going to "surface" the plated cylinder wall?

 

[ACGUY]

We finished the rebuild today, and the bike runs like a scalded dog. That works well. I had to scotchbrite the cylinder a bit to knock down a few glazed areas, and returned the bike to the stock main jet. We rode it for about 2 hours easy to break in the rings, and wow, what a power difference. The low end is incredible, and the bike wheelies with no effort. We almost had a snafu when completed because we figured out the throttle cable was frayed badly at the gooseneck near the carb cap. (CHECK YOURS) The bike owner was happily out testing his fresh new top end, and the throttle stuck wide open on him due to the trapped cable frays. I think he pinched up his seat cover a bit.
I learned a few things from this excersize:
When you buy a used bike, look it over real well when you get it home.
KDX's are EASY to rebuild, and it started up on 2nd kick after rings installed.
The KIPS however is a poor design, and there are lots of potential failure modes with the valve. Even after being cleaned, it still sticks a little.
Check your control cables periodically, especially at weak points, and bends.
Ride safe, have fun, and don't neglect the maintenance that your bike needs to keep you safe, and having fun.
Email to [email protected], if you have any questions or comments about this article.