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1994 KDX 250 Issues

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Hey all,

Just bought myself a 94 KDX 250 (slight basket case) and im having a couple of issues with it.

Firstly, it bogs rather badly going from idle to WOT. It starts and idles fine, and has no problem in top end power. So before i start messing around with anything i just wanted to make sure that adjusting the jet screw outwards would be the first thing worth a try... and also, how far out is too far?

As far as im aware, the jets are stock.

Secondly, the bike had been sitting for a while before i got it, and it seems like the clutch is binding up. But the strange thing is, when you click it in gear at idle it feels like it wants to pull away, but if you rev it up it stops wanting to pull away untill you let it go back down to idle. Is that the sign of it needing the fibre disks oiled up or should i put a new plate kit through it?

Thanks! :bonk:

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Hey all,

Just bought myself a 94 KDX 250 (slight basket case) and im having a couple of issues with it.

Firstly, it bogs rather badly going from idle to WOT. It starts and idles fine, and has no problem in top end power. So before i start messing around with anything i just wanted to make sure that adjusting the jet screw outwards would be the first thing worth a try... and also, how far out is too far?

As far as im aware, the jets are stock.

Secondly, the bike had been sitting for a while before i got it, and it seems like the clutch is binding up. But the strange thing is, when you click it in gear at idle it feels like it wants to pull away, but if you rev it up it stops wanting to pull away untill you let it go back down to idle. Is that the sign of it needing the fibre disks oiled up or should i put a new plate kit through it?

Thanks! :bonk:

I just purchased a '95 KX250. Exactly the same problem(s). The stock jetting is definitely fat. It runs great at WOT. It was suggested to me to 1. change tranny fluid 2. Check length of clutch cable, for wear & stretch. Have been too busy riding or working to figure it out. I did purchase a good lookin' bike for next to nothing. Good luck:ride:

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the KDX250 is a different animal from the KX250s. It was a poorly jetted, to low of compression, to much airbox restriction and poorly suspended. Here is my "how to" get the bike to be a screamer when I had one:

.26" headgasket (88-91 KX, raises compression)

remove the intake restrictor on the top of the airbox

Jetting: 38/158 , R1367H needle 3rd clip from top, #6 slide

a pipe and silencer will finish off the power for the bike. Be sure to have a fresh top end and cleaned power valves. Inspect the gears, replace as needed. Also inspect the reeds. I ran the Vforce that gave it a great mid to top hit on the bike and still able to lug it out.

Rear shock was not bad, but I ran an ohlins. Then swapped to a set of KX front forks, wheel and tossed the odometer. The stock forks do not have a rebound adjustment and really need them. Dont waste money on the stockers. Get a 95+ kx250 front end (clamps, brake, wheel, forks and other misc parts) and swap it over.

Great bike after that! a bit large in the frame, but had plenty of power with the WR tranny. I ran 13/50 gearing with great sucess from track to trail to desert.

Here is the rest of my notes on the where parts interchange from to help finding aftermarket parts like the Vforce reeds:

Where parts come from:

Keep in mind that the 91-94 KDX250 was built off the 88-91 KX250 bike mainly. There are some differences between the bikes, but if you get stuck trying to find a part, be sure to cross reference that bike first. There are also a lot of bearing and clutch parts used of the KX500s of the same years.

-pads and rotors are the same as the 89-02 KX125/250/500 for the 91-94 kdx250. So you can get the ceramic pads and wave rotors there. Brake lines seem to be different though same with the MCs. You can run the KX front and rear SS aftermarket brake lines without issue.

-Steering head stem bearings list the same for the 80-91 KX250 and KLX250 94-96

-For the Fork seals, l the 88/91-95 KX250, KLX250/300 fork seals list the same as the KDX250 units (43mm units). The stock is a 43mm ID x 55mm OD x 9.5mm height. you can run the 10.5/11mm tall seals for beatter sealing. Be sure to also install some seal savers to prolong the fork seal life.

-Fork gaurds is the same as the KLX250/300. You can run the 90-93 KX units also, but they offer no side protection to the forks

-Brake Pads: KX125/250/500 89-93

-Rear brake holder/bracket -- same as 89-94 KDX200. Use this for the rear shark fins & scotts gaurd

-Front Forks: Kayaba. .35 kg for 92-94, .34kg for 91. 43mm inverted. (similar forks as the KLX 250/300 bikes)

-Rear shock: 4.8kg for 92-94, 5.0kg for the 91. Spring same for 88-02 KX and 89-94 kdx200. Eibach 996 series

-Sprockets seem to be a KX/KDX thing. No differences there.

-aftermarket Chain rollers = Small

-Chain Guides: 88-96 KX 250/500, KDX200

-Reeds are the same as the KX500 units in FMF. Boysen same as 89-96 KX250. Mototassinari use the KX500 VforceII kit.

-Lower shock bearing/seals is the same a 88-01 KX500

-Unitrak bearings are the same as a 88-01 KX500

-Rear swing arm slider is the same as the 94 kdx200 , 89-01 KX500

-Rear mudflap is the same as the kx250 (90-91)

-Looks like the seats are a bit different, but a cover would most likely fit both From a 91-94 250 or 89-01 KX500.

-Clutch: 89-01 KX500, 88-91 KX250

-Clutch cable 90-91 KX250

- Throttle Cable : 88-91 KX250, 88-02 KX500

-Top End gasket, same for 88-91 KX250 (stock thin head gasket .26")

-Piston Needle Bearing 74-02

-Connecting Rod 78-02 KX250

-Piston & rings KX250 90-91

-Here is what interchanges on the rear bearings:

Timken 104 series bearings. You can pick them up at any autoparts store.

1986-2002 KX125/KX 125/KX250/KX 250 and KX500/KX 500, 1989-2002 KDX200/KDX 200/KDX220/KDX 220; 1991-94 KDX250/KDX 250; 1993-96 KLX650A/KLX650R/KLX650/KLX 650; plus the 1983-84 KL250C/KLR

-Front bearings:

Timken 202 series bearings. You can pick them up at any autoparts store.

KAWASAKI: 1983-83 KX125/KX 125; 1968-70 F3 175; 1983-96 KDX200/KDX 200 1969-70 F4 250; 1971-72 F8 250; 1973-75 F11 250;1982-84 and 1991-94 KDX250/KDX 250; 1994-95 KLX250D/KLX250R/KLX250/KLX 250; 1970-75 F5/F9 350; 1993 KLX650A/KLX650R/KLX650/KLX 650; 1993-96 KLX650C.

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Thanks for all the info JJRace, but at the moment i just want to get it running to the point where it's ridable.. im actually gonna be putting it on the road, so it won't need to have crazy power and performance... just yet. :bonk:

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thats the problem, you will have to do the airbox, carb mod and swap head gaskets to get it to run properly.

also inspecting the top end, cleaning the power valves is a must for getting it running properly and inspecting the reeds.

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:banana: Excellent post JJRace! :smirk: Your jetting and mods are spot on with what I have done with mine. BTW, are you member over at KDXrider.net? If not, would you mind me cross-posting your post to that forum to share with the members there?

Firstly, it bogs rather badly going from idle to WOT. It starts and idles fine, and has no problem in top end power. So before i start messing around with anything i just wanted to make sure that adjusting the jet screw outwards would be the first thing worth a try... and also, how far out is too far?

1.5 to 2 full turns if your pilot jet is correct.

A few questions so we can help you...

Is your air filter clean?

Do you have a fresh spark plug, properly gapped, and installed correctly?

Do you have clean and fresh fuel mixed with a quality 2T oil? (not mixed in with old fuel)

Is your carb clean and in good working order? (float level correct?)

Is transmission fluid disappearing?

Is it dry behind the stator cover?

As far as im aware, the jets are stock.

You need to open it up to find out for sure. When you do, you need to write down what main and pilot jets you have along with what needle and slide it has. All your changes will go from there. The '91-'94 KDX250's were known to be horribly jetted from the factory. Opening up the air box like JJRace suggested, changing the slide from a #5 to a #6, and then following basic jetting procedures should get it running pretty good as long as everything else is working properly and in good shape.

Secondly, the bike had been sitting for a while before i got it, and it seems like the clutch is binding up. But the strange thing is, when you click it in gear at idle it feels like it wants to pull away, but if you rev it up it stops wanting to pull away untill you let it go back down to idle. Is that the sign of it needing the fibre disks oiled up or should i put a new plate kit through it?

Lets start with the easy stuff and go from there. Have you changed the fluid since owning it? What are you using for fluid, M/C rated trans oil, ATF Type F, or ???

Thanks! :bonk:

You're welcome! If there is anything I can do to help just let me know!

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Great info JJrace!

Furball: You really need to re-work the carb to get it to run right. Jets/slide/needle.

Everything that JJrace said is correct. I had a KDX250 for a few years. I went through all of these modifications on mine as well. You will never get it to run smoothly without the carb work.

The head gasket and exhaust help a lot too. You will love that motor once you get it tuned correctly.

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Thanks muchly guys, i'll be sure to go through all your suggestions as funds allow for it. Carb and clutch are first on the list.

Can i get away with rejetting the carb and taking the restrictor out of the airbox without changing out the expansion chamber and muffler... or are those mods pointless with the stock exhaust set up?

Somebody asked about what oils are being run in it, and all i know is they're "good synthetic oils"... as i was told by the guy i got it from, i don't think the oil has actually seen much ride time, but it may have been sitting in the bike for a while... does oil go bad?

Is your air filter clean? Yes

Do you have a fresh spark plug, properly gapped, and installed correctly? Yes

Do you have clean and fresh fuel mixed with a quality 2T oil? (not mixed in with old fuel) Yes

Is your carb clean and in good working order? (float level correct?) Haven't stripped it down yet

Is transmission fluid disappearing? No

Is it dry behind the stator cover? I think so... im getting assloads of spark so i dont *think* the stator is being fowled up by anything.

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he wants you to look behind cover to make sure you dont have a leaky crank seal.

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Sounds like the carb is your target. Lotsa good info in this thread.

Mine actually runs really well with the stock jetting. It came with an old gold series pipe, a turbine core hockey stick and has a .026 gasket with fresh top end. Airbox all stock. Idles nice with smooth transfer on the power valve. Lots of power but falls off rather quickly. I havn't felt the need to mess with it much. It "feels" as fast as my 450 although I'm sure it isn't. Very fun bike.

Edited by Kroynon
sp.

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you need to tear open that carburetor and rejet that bad boy. thats the only real problem. Go by his jets listed above and start there. once you get that sorted out then you can adjust your run settings.

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Yep, gonna try and source the parts tomorrow and hopefully do the carb rejetting and stuff while im on night shift tomorrow night.... what else am i supposed to do all night by myself, work? Pfft. :bonk:

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Jetting will be different for each bike and elevation, but here is what I ran in mine to get it ripping:

Pilot 38

Main 152

Throttle Slide #7

Needle #R1370H

Stock is: Pilot 42

Main 165

Needle R1368H

Throttle Slide #5

Stock setting is usually way too rich. Mine ran like crap in stock form. It ran good when I opened in up, but was really rich everywhere else. It was very "boggy" throughout the entire throttle range. It felt like it wouldn't rev correctly and fouled plugs every time I rode.

This is the entire setup I ran:

Carb setup (listed above)

FMF Gold Series Pipe

Answer SA Pro Silencer

Boyesen Power Reeds

Wiseco Top-End

Thin .026 KX Head Gasket

Just getting the carb setup correctly will make it run right. Adding everything else will help as well, but the carb setup is what is making it run poorly.

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PLEASE HELP....

 

I've had a 91 KDX 250 for the last two seasons with chronic bottom end challenges... very boggy and unpredictable power band.  Decided to rebuild the top end this past winter.  Replated cylinder, new piston, rings, needle bearing, wrist pin, power valves, Boyesen power reeds, .026 head gasket, Fatty pipe and Power core muffler, pilot 40, main 160, stock #5 slide, (weird) needle on bottom clip, new transmission oil and fresh mix as well.  

 

I finally got it all back together a few days ago and fired it up for 'break in'.  Let it run for approx 10 min... and it was amazing!!!!!  Felt like a completely different bike.  Beautiful idle, perfectly linear throttle control (just idled it around back yard).  Then, after parking it, it decided to rev high, as if it was running empty (this is what I assumed because I filled it with very little fuel), so I switched it to reserve and it ran like crap.  Still runs like crap.  

 

I have plans to instal a #6 slide and maybe even lean out the jetting.  But wondering if I need a whole new carb (happy to get one if it will solve my problems)?  The 'weird' needle was installed by a local shop last year, and it did run a little better with this mod.  

 

The BIG questions are...

 

Why did it run PERFECTLY for the first 10 min then turn to crap?

What determines a 'worn out' carb?

 

Thanks in advance.

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40 pilot is too rich. Get a 38 and send your slide off to be cut to a 6 or 6.5. That will fix all your problems with jetting. Run 40:1 to 50:1 and run the stock needle with the clip in the highest position. The compression that you went to with the smaller basket gasket requires premium gas at least and also the reed and pipe you put on with dramatically change jetting on that bike. You need to LEAN it out!

To answer your big questions...

1. It was not loaded up when you first started it after your rebuild, lugging it made the problem arise

2. Carbs do NOT wear out. So that is not your problem. It can only be your cable or throttle system that makes your carb feel worn out. Don't &%$#@! foot the thing after a fresh top end, I know people have there own break in procedures, but you need to almost ride it like how you normally are going to ride it. Don't let it get too hot though. Take it out and blowout it out well next time it runs. Just use a flat road of any kind and buzz up and down once or twice. Don't pin it and tap it though just rev it out a little bit, because it's still fresh!

The jetting on these things is a marvel of how did it ever run from the factory kinda thing.

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