The tale of two CARBS

[mdecesari]

I have two KDX-200. Both jetted identical. The 96 KDX runs perfectly. The 95 runs very sluggish just off idle, and when you decel quickly the engine tries to die and does not respond to the throttle until past 1/4 throttle. I took the carb from the 96 and put it on the poor running 95 and the bike ran perfect. As a process of elimination I moved from the 96 KDX one part at a time, the main jet, pilot(slow) jet, float bowl and float valve. None of the parts moved from the 96 made the 95 KDX run good. I put in the jets, float valve and needle, from the 95 into the 96 carb and the bike ran perfect. I seem to have norrowed the fault down to something in the 95 KDX carb body itself. I took the 95 carb apart and cleaned it with carb cleaner and compressed air, but the cleaning did not help. I am not runling out that the carb has a factory defect because it had a 35 pilot jet in it when I bought it used. The previous owner may have been trying to lean out the blubery low end.
The 95 runs ok on the mid to top end. Just off idle to 1/4 throttle is where it runs poorly. The bike will not idle easily. When I put the 96 carb on it idles fine and runs much cleaner off of idle. The needle jet is set the same on both bikes so I don't think the needle jet is the problem.
I am completly stumped and would appreciate some advice on fixing the carb or a good recommendation to send the carb in for repair.

thanks

 

[Mac]

Your choke could be sticking open a little or the float needle seat could be worn. Either of these would cause the bike to run rich.

 

[mdecesari]

I changed out he float needle from the 96 to the 95 and no change. I will change out the choke circut and see if that works.

Thanks

 

[Robcolo]

It sounds like it's going lean , not rich. check the pilot passage in the carb body. Get a "tamper proof" torx [#25 I think] and remove the needle jet holder assembly accessible by removing the float bowl. There's likely some dirt inside those small passages.

 

[Canadian Dave]

There are three o-ring under the jet block, between the jet block and the carb body. Follow Robcolo's instructions and remove the jet block, inspect the o-rings to insure they aren't damaged and insure there isn't anything obstructing the flow of fuel. Chances are fairly good one of the o-rings wasn't installed properly or is damaged. If you can't find the proper tamper proof bit you can carefully drill the center pine from the torx bolt. Be sure to clean the carb again to insure you remove all the metal filings.

David

 

[mdecesari]

I changed out the choke circut and the 95 did not run better. I will try to get some no tamper torx and clean out the jet holder assembly. Thanks for the advice. I will get the tools tomorrow and let you know how this turns out. Where can you get new rubber O-Rings?

thanks,

Mark

 

[Lorin]

Just a shot in the dark, but are the slides in both carbs the same? How about the needles? I didnt see what kind of bike the other carb came from and thought that maybe the slides or needles were different. Maybe even a clogged vent tube?

 

[kdx357]

float level or clogged jet maybe

 

[canyncarvr]

NOT RECOMMENDED FOR SMALL CHILDREN ...or unsupervised adults..

BUT..

I've used a common screwdriver to lever against a safety torx center pin to just snap it off. It would take a far better drill handler than I to use a bit to do it (and not damage the rest of the screw). The shape of the torx recess gives you a great place to lever against, too.

 

[mdecesari]

Bingo! It was the rubber o-rings under the jet holder. I bought a set of tamper torx heads needed to remove the jet holder. The O-rings were dried and flat, i.e. no seal. I got some small o-rings from ace hardware for a temp fix. New o-ring set from Suddco on the way. I knew when I bought the 95 KDX that it did not have many miles on it, original chain that had not ben adjusted yet and original tires so I think the bike sat for a long time with the dry Tucson weather the o-rings just dried up and went flat.

Thenks for all the help, I was stumped.

Mark DeCesari