Kx100 wont stay running without 1/2 throttle

[Bron-Yr-Aur]

good point.  not exactly a ringing edorsement for the v force reeds you have used.
I had a bad float valve in my kx250, it wasn't grooved or anything, visual inspection looked great, but ethanol gas had apparently eaten at it a bit, and it didnt run crisp at all.  It never really leaked out the overflow.  
If you lay the bike all the way over does fuel come out? I have incorrectly set float heights before because i wasnt careful to make sure the plunger on the float valve wasn't compressed while setting.  this caused my floats to be set way to low and the bike was starving for gas at upper rpms. kinda the opposite of your problem i guess, but you never know.
Do you have a timing light you can use or borrow?  I'd be curious to see if it's staying within the timing mark when you have it running briefly.

Hmm that's something to think about. I didn't think about the plunger issue. It might not be right. No, fuel doesn't come out. But I didn't go way over. I have the carb off and apart right now, so I'll look at it tomorrow. I'm out of carb cleaner, so it's on the bench right now in pieces.

I don't have a timing light, but I believe I could borrow one. I may go that route this week if I don't make any headway.

Thanks, buddy.

[DylDog]

The plunger can be a bit tricky when adjusting the floats.  hold the carb at an angle so the floats will rest on the plunger but not collapse it under there weight.  You may need to take the floats on and off a few times before you get it right.  Hope you get this figured out soon, riding season is approaching!

[Bron-Yr-Aur]

The plunger can be a bit tricky when adjusting the floats.  hold the carb at an angle so the floats will rest on the plunger but not collapse it under there weight.  You may need to take the floats on and off a few times before you get it right.  Hope you get this figured out soon, riding season is approaching!

Yep that's how I did it. I checked again today and I just tilted the carb until the float stopped swinging freely. I think it may be set a little low though. Now when I tilt the bike, I can't get any fuel to pour out the overflow. Might need to readjust it.

Today, after cleaning and reassembling the carb, i removed the silencer just to make sure there's no blockage. Same. I started the bike and held my hand over the exhaust. Raw fuel started to collect on my fingers.

Thursday I'm going to try swapping the CDI with the neighbor's. I'm confident that's not the problem, but if I have to take this to anyone, I want to be able to eliminate everything that he'd want to try. Sad part is I don't know any mechanics that I trust.

[351mustanger]

If it is shooting excessive raw fuel out of the exhaust, and jetting is close, you are having a weak or intermittent spark issue. If your coil is testing bad, I am not sure why this isn't the top item on your check list. 

[turbo dan]

Raw fuel out the exhaust is screaming "carb issue" to me.  Where ever you have the floats set, set them lower.  Go way lower and work your way back up.  Make sure nothing is binding them up or interfering with their movement when the float bowl is installed.  Make sure the floats close the needle valve when they raise by hooking the gas line up to the carb with the float bowl off and raising the floats by hand.  Make sure the floats are still buoyant.

There has got to be something out of whack in that carb.  Crankcases don't fill with fuel and start shooting it out the exhaust because of an ignition problem.

[351mustanger]

I don't think the case is flooding. I have seen first hand, an ignition problem cause raw fuel to come out of the exhaust. It was coming out like spray paint.

[YZPaGuy]

Check the brass piece that screws into the top of the carb. My son used to snap them when running a big tank. I always kept a couple extras on hand. It will make the slide bind and let dirt in the top of the carb.

[Bron-Yr-Aur]

Check the brass piece that screws into the top of the carb. My son used to snap them when running a big tank. I always kept a couple extras on hand. It will make the slide bind and let dirt in the top of the carb.

I actually just installed a new throttle cable, so that's good. With the higher bars, I was nearly getting binding with the short cables. I had a spare YZ125 cable, so I stuck that in there. It works great. Now I wish I could figure out what longer clutch cable I can use.

Raw fuel out the exhaust is screaming "carb issue" to me.  Where ever you have the floats set, set them lower.  Go way lower and work your way back up.  Make sure nothing is binding them up or interfering with their movement when the float bowl is installed.  Make sure the floats close the needle valve when they raise by hooking the gas line up to the carb with the float bowl off and raising the floats by hand.  Make sure the floats are still buoyant.
There has got to be something out of whack in that carb.  Crankcases don't fill with fuel and start shooting it out the exhaust because of an ignition problem.

Well, Dan, you're the man. Solved the problem! And you were the closest. It was a carb issue. Well, technically user issue. (Sigh) I wish I didn't have to admit this, but you guys have been strung along for so long, I have to confess my stupidity.

I was testing the float, fuel inlet etc. There were no problems, everything checked out. So I started really examining the carb. Then it hit me... "Where's the bloody needle jet!!!" It should've been obvious, but one of those things that I don't notice unless I'm looking for it. In defense of myself, I never took it out. I never remove them, because they're such a pain to get out - usually. It must've fallen out during my first cleaning, and I have no idea where it is. I'll try to chase on down tomorrow.

Thanks so much guys for walking me through all this. This was a learning experience for sure.

Btw does anyone know the range of carbs that use the same jet? I have a spare Keihin from my KTM 200. I haven't pulled it apart yet to check.

[turbo dan]

The needle that drops into the slide or the big brass piece that the main jet screws in to?

Sounds like you're getting close.  Too soon to say its fixed until its running right again but this sure sounds like the problem.

[Bron-Yr-Aur]

The needle that drops into the slide or the big brass piece that the main jet screws in to?

Sounds like you're getting close.  Too soon to say its fixed until its running right again but this sure sounds like the problem.

The needle jet itself. The brass piece that presses into the bore of the carb and is held in place by the main jet holder (emulsion tube). I've never seen one come out. I feel stupid because the tip of them, where the needle enters, is very visible when eyeing through the bore of the carb. It definitely makes sense. Without the jet, the needle is just swinging freely, nothing to seal up against. So unmetered fuel is just pouring into the carb through the main jet.

I sure hope that's all there is. What scares me is that I thought I remember seeing that during my travels through this carb. If it happened the first time, that means I've been through this carb 3 times without seeing the missing piece. But my ADHD has left me looking stupid before. Times that I SWORE I saw something, or didn't, and the opposite was true. Oh well.

Thanks again!

[nobade]

Glad you found it! You have been keeping me wondering for some time now. The one in your KTM carb is not removable but the Kawasaki dealer or jetsrus or RMATV has them available.

[351mustanger]

Whoa! I didn't see that coming. I was wondering how it could have fallen out, but see it doesn't have a mechanical fastener to hold it in, just the cap keeping pressure on the return spring. I have found discounted needles (compared to kawasaki price) and ones that have been discontinued here:

 

http://www.motorcyclecarbs.com

[Bron-Yr-Aur]

No it wasn't the needle that fell out of the slide. It was the jet in the bottom half of the carb. When you're looking through the carb, you can see the upper tip of this jet poking up from the bottom of the bore. It looks like a little brass tube that the needle slides into when the throttle is closed.

[nobade]

That is a good thing about the PWK 28, that needle jet is replaceable. On your 38 it's not, that is why I have a 28 on my KTM now. Once it is worn on the big carb you get to buy a whole new carb.

[Bron-Yr-Aur]

That is a good thing about the PWK 28, that needle jet is replaceable. On your 38 it's not, that is why I have a 28 on my KTM now. Once it is worn on the big carb you get to buy a whole new carb.

Sheesh that's a crappy scenario! I didn't realize that.

[DylDog]

The pilot jet you are referring is replaceable on the pwk38 as well.  That makes slot of since.  If you have a spare from your ktm it should work if it's the correct size, I think both use a 21 series jet.  Keihin only uses two different types of pilot jets.

[nobade]

He's not talking about the pilot jet, but rather the needle jet. It is pressed in on the PWK 38, and held in place by the main jet holder on the PWK 28.

[DylDog]

My mistake

[YZPaGuy]

Lmao, important part is you found the problem before pushing it off a cliff!

Great story for the bench races!

[Bron-Yr-Aur]

Thought I'd give a quick update. I ordered a carb kit from RMATV because, according to the girl on the phone, "I just called out to the warehouse," after 5-10 min on hold. "The guys out there verified that the needle jet is indeed in the kit." You know what's next right? It wasn't.

 

I called back. Told the guy what was up.

"That's not in the kit," he says.

"I know! That's why I'm calling you!" (Head slap)

So I'm getting a refund for the kit.

 

I find another kit in eBay for $36. 10 bucks more than RMATV, but just the jet alone from them was almost $30. So I ordered the kit. That was on Sunday. On Tuesday I'm pulling out my KX250 for a potential buyer. My son exclaims "look what I found!" Yep, the jet. I had apparently kicked it back under the tire. (Head slap again)I haven't even received the carb kit yet, but I have his bike back together and it's running great.

 

Anyone want a carb kit for a PWK28? Lol