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I just rebuilt the topend. Carb was rebuilt. But the bike wont run correctly. It idles and cranks perfect and if you rev it slow it will rev a little then bog. If you give alot of gas it bogs then dies. It wont go into the powerband. It has a new spark plug. And the piston IS in the right way. Rings are good. Compression is where it should be. I have tried everything but it just wont run right. The only thing I can think of is the power valves? I just need someone elses opinion.

Carb was rebuilt how exactly? A thorough tear down and cleaning, followed by rejetting hopefully? Rebuilt top end will require you to rejet, and it definitely sounds like a fuel delivery problem. Power valves it would run normally below 6k and then feel flat, but wouldn't affect throttle response if everything is in poper working order.

Yes everything was cleaned and Ive rejected it. And I fixed my float level. New reeds also

Sounds like something stuck in your main jet or the float is adjusted too low...other possibility is your needle wasn't attached properly and it is just lodged in your main. Take the carb apart and inspect, it sounds like a fuel issue.

Thats what I thought so I had a shop check it out and they assured it wasnt the carb but they didnt find anything else wrong with the bike either so Im stuck with it

I had a problem almost exactly like you're describing when my main jet was blocked. Even if the carb has all been apart and redone, can't hurt to pull it off (very easy on a KDX compared to other bikes) and blow some carb cleaner / WD40 / air through the main jet.

so, you rebuild the top end and the carb yourself and then had a shop inspect the carb?
or did the same shop that checked the carb rebuild it?
(people seem a lot quicker to point out the mistakes others make, rather then their own)

if we are all in agreement it is a fuel delivery issue AND your carb is clean then the only thing keeping the fuel from reaching the cylinder is the reed block
after you clean/check/or replace the main jet the next step might be inspecting the reeds

come to think of it, you claim you rejetted the carb, but I don't see how you could go through the process of rejetting it if it isn't running right?

was it running fine before you installed the jets that are in there now?
or did you have issues with it with each jet you tried?

This thread kinda gives off the 1950's police interrogation room vibration

"So tell us Joe, did you rebuild the bike yourself or did you pay someone to do the job for you??!"

HAHAhhahh...

It does, I admit...but when someone just blurts out "it don't work, what can I do to fix it?" what else are we to do? Being as simple as these bikes are, and as bullet proof as the motors are, fuel delivery issues are 75% of the issues people have (based on my highly scientific WAG method). Plus I can't count the number of times we have said "reclean the carb, rejet after everything else is mechanically sound" only to have the poster go off and replace bits and change things and fuss and cry, and eventually come back and admit "it was my jetting". It think DIY is spot on with his line of questioning. I love to help folks out and keep the green beasts running, but you always hope that at the least they've been through their manual, and done due diligence. Then again that could just be the engineer in me

Yes they are a cakewalk to diagnose these bikes. Almost any problem can be solved within 25 minutes even if it means taking the whole top end apart to find out...

I just got back from my brother's place helping him with his '04 crf250r...There is almost nothing conventional about those bikes compared to a KDX. I must have asked him "what is this thing?" about 10 times lol. Cam chain tension adjusters, compression relief switches, 3 different CCV hoses.. He told me he spent over $600 on top end parts; piston, shims, valve seals, etc and having the forks rebuilt. Twice what I've put into my bike rebuilding the top end, suspension, wheel bearings, and seals lol

Made me feel lucky to be riding a KDX. Said he's finished with 4 strokes after this season lol. His next bike will be a 2 stroke heheh

Joe13Duck: Take your carburetor off, empty the fuel out of it, flip it upside down and take the float bowl off. Check the little etched number in the side of the main jet. Have a look down the center of it and see if there are any obstructions. Also look at the float level and make sure it 16mm +/-1mm from the bowl contact surface to the top of the float.

Gotanubike wrote:This thread kinda gives off the 1950's police interrogation room vibration

just remember [german accent] we have ways of making you talk [/german accent]

Modern day German enhanced interrogation...what might that include? Being locked in a room and fed nothing but wiener schnitzel until you fess up?

One item not mentioned in this thread is the carburetor jet block gasket. Past posts report they can degrade when exposed to carburetor cleaner, and cause mysterious performance problems.

pumpguy wrote:One item not mentioned in this thread is the carburetor jet block gasket. Past posts report they can degrade when exposed to carburetor cleaner, and cause mysterious performance problems.

x2

True, when you rebuilt your carb did you use spray cleaner or a dip tank? most dips will kill the jet block gasket, but the spray cleaners are fine. Once that gasket is compromised you will NEVER get it to run right until it is replaced.