'91 KX 250 no idle!

[Racinante]

I just bought a used '91 KX 250. I have replaced the pipe (old FMF folded in half) with a new DG, cleaned the carb and quite a few other things. It runs great! But, I can not get it to idle at all. Well, that's not exactly true. When I first start it up, it will idle. But, the warmer it gets, the less it wants to idle. This is all with the lock nut removed so I can screw the throttle stop in all the way. The more I back the mixture screw out, the more it acts like it wants to idle, but if it's completely warmed up, it just dies as soon as the revs get low.

When I bought it, it had: 160 main, throttle slide 7, needle jet is N85B with clip 2 positions from the top, and pilot jet 55.

The only differences than what the Clymer manual lists as stock is: throttle slide 6, needle jet N85C at position 3, and pilot jet 58.

I have since moved the needle clip up one position (lengthening the needle) and it runs much better!

Would the throttle slide make a difference on idle. The throttle stop screws in a lot before it even begins to move the throttle, and at max (no lock nut) there's only about a 1/2 mm gap between the bottom of the slide and the carb. What's different between a 6 and a 7.

Which is a leaner needle, B or C?

Could my pilot jet be too lean or too rich for even moderate idle?

Any info would be awesome!!!. This is my first MX bike, and I've been waiting about 2 months to go riding with friends.

 

[crazycr125]

did u adjust the idle screw? and it wont hurt anythin with no idle.

 

[spanky250]

You need a leaner pilot. The fact that the more you lean the airscrew, the more the problem improves, should tell you that the pilot is too rich.

 

[Racinante]

Hey thanks Spanky!

That was one of my suspicions, but I wasn't exactly sure. It has a 55 and I guess Kawasaki only offers one size leaner, 52. But before I go that route, I do need to replace the pilot air screw. It's scored around the tip as if it was screwed in too hard. I didn't really think that would make that much of a difference, but I guess it does.

Thanks for the info though. I wasn't sure if screwing it in or out made it leaner.

BTW, was my opening statement too long?

 

[spanky250]

After reading your post again, I caught something I had missed earlier. You say it has a 7 slide in it now? Unless I've gone brain dead, that is richer than stock, and I can't imagine a Kawie needing anything richer than stock. That engine is very similar to mine in a lot of ways, and the fix for my poor small-throttle performance was a leaner slide. I wonder if your carburation problems wouldn't be much improved if you went back to the stock slide. I still think your pilot is rich either way, and unless that carb is less similar to mine than I think, you should be able to get a smaller pilot than a 52. I can get a 35 for my carb, and in really hot weather, I run a 38. Of course the bikes aren't identical, and my carb is smaller than yours.:D

 

[Racinante]

I'm glad you brought that point up. The pattern I have seen with the Clymer manual is that as the numbers get bigger, the mixture gets richer. This is true for the Pilot and Main. But, it says that as the numbers get bigger for the throttle slide, the mixture gets leaner. Could this be a misprint? It doesn't seem logical that they would change just for the slide. Do you remember the numbers for your slides? If you've purchased a new slide, then you'd be the one to ask.

Also, how does mixture relate to changing the jet needle. I would assume A would be leaner than E. I have a B in now, and the clip is at it's leanest setting. Stock is a C. If you are right about the slide deal, I might be overcompensating with jet needle.

These are the pitfalls of buying something that someone else has already messed with, but it is a massive education for me. I've learned so much in the past month! And I definitely appreciate your help!

BTW have you ever had problems with your ignition coil? I'm having a connection problem with my spark plug boot and wire. It's obviously been messed with.

 

[spanky250]

I went back through my papers, and you are right, the larger number on the slide signifies a larger cutout, hence a leaner mixture from idle to about 1/3 throttle.

When I bought my bike, the former owner had tried rejetting it, and obviously had no clue what he was doing (he had also blown the engine and had the cylinder sleeved, but that is another story). It ran horrible, and would not idle, even with the airscrew all the way out and the idle screw all the way in. The bike only had 120 miles on it, but the pipe had so much oil in it, I pulled the pipe off and dumped about a cup of oil out. I found the air passages at the intake mouth of the carb completely clogged with filter oil, and after going from a 45 pilot to a 38, and cutting my slide to make it leaner (a new slide is $90 :eek: , so I modified the existing one), changing the main from a 170 to a 165, and replacing the needle with the next-leaner one in the second groove from the top, I now have excellent low-speed running manners, nice plug color, very clean, spooge-free running, a perfect idle at such a low rpm it amazes people that it doesn't die, and my bike never loads up or fouls plugs no matter how slow I ride or how long I keep putting around.

I suggest you start with the pilot circuit first before changing anything else. You may also want to check the float height, my bike is very sensitive to a too-high float setting, it makes it very rich down low. I would also check to make sure the enrichener plunger is sealing properly, if fuel leaks past the seal it will make the 0-1/4 throttle opening very rich.

 

[Racinante]

Checking the enricher plunger was one of the things i did when i first took the carb apart. The rubber looked perfect! I have already checked the float height with the float measurement method, but it is not as accurate as using the tube method connected to the cap at the bottom of the float bowl. I would like to check into this. Hopefully I could either buy the piece to do it, or make my own with a cap from the junk yard.

I looked on "Buy Kawasaki's" web site and it seems for the KDX they used a richer slide, richer main, and leaner pilot. Your 38 pilot is the leanest they list for pilots. 52 is the leanest they list as an option for mine, and that's two steps lower than factory specs, just like yours. I might try that, but only after I am positive my floats aren't letting in too much fuel.

How did you arrive at 38 for your pilot? Did you buy everything else down to that, or just try 38? I'd like to know what characteristics to look for that would warn me of a too lean condition. I don't want to seize it.

But, I do need to do something cause I just fouled my second plug. Do you know if carbon and oil can foul a plug to the point that it still won't work after cleaning? Also, what size is your slide? You custom cut it yourself, right? Luckily, Honda-Kawasaki.com can sell me one for $65! Hopefully I'll just have to lean the pilot out. Every other throttle postion is excellent.

 

[spanky250]

Originally posted by Racinante
How did you arrive at 38 for your pilot? Did you buy everything else down to that, or just try 38? I'd like to know what characteristics to look for that would warn me of a too lean condition. I don't want to seize it.

When I bought the bike, it had a 42 in it, and was very rich on bottom. I tried a 40, still too rich, so I bought the 38. This was still borderline rich on hot summer days, so then I modified the slide by grinding 1mm off the cuttaway to allow more air to flow, this setup changed the whole nature of my engine. It became clean and tractable, and never loads up or acts weird.

Don't worry about going too lean with the pilot, you can't hurt the engine like going too lean with the other circuits can. The worst thing that will happen is it will bog when snapping the throttle open, and maybe be hard to start.

 

[wanrep]

I would agree, you're pilot jet is way too rich. I'm not sure why Kaw put such a rich jet in. The 1990 came stock with a 7 slide and a 55 pilot. My '93 came with a 7 slide and a 50 pilot.
I've had to go leaner 2 sizes on the needle and down to a 42 on the pilot to get mine running crisp for woods riding here in Missouri.
It's usually not wise to make big jumps rejetting but try a 50 pilot jet. You may even need to go smaller.
It's normal to have a higher idle when you start it cold but you should be able to get it to idle when warm.
Air screw should be 2 turns out.
If you haven't repacked the silencer, do that also. It will make a difference.
If you've got good plug color and it runs well other than idle, just change your pilot jet and and you should find some idle.
As for the spark plug cap, it unscrews from the wire. Unscrew it and cut about an eighth of an inch off the wire and screw the cap back on.

 

[wanrep]

Forgot to mention the float level....best way to set it is by fuel level with it assembled.
I used an old float bowl cap and needle jet tubing to make a guage.
I got the correct fuel level by setting the float height with the carb upside down and the needle tip compressed, contrary to what the book said.

 

[Racinante]

Thanks Wanrep.

I have an old carb off a Yam 175 enduro, and I'm gonna see if the bowl cap from it will fit my KX, in an attempt to make a fuel level gauge. I do think that could be part of my problem. If it doesn't fit, there are a couple of bike junkyards around that I could probably find an old cap in.

About setting the height: The book does say to adjust it where the needle first makes contact, "without compressing". If I adjust it compressed, that should give me a lower fuel level right? The way it is set now, I sometimes see a lil' fuel drip out of one of the drain tubes when I lean it over on the side stand.

Oh Yeah, I think I might order the jets from Honda-Kawasaki.com. They need the part number from buy kawasaki.com. They only list down to a #52 pilot for a '91. Could I just use part numbers from other years to order the smaller jets. They all have the same first five digits. The four numbers at the end, after the dash are the only thing different. I'm going to check prices at a couple of local shops today, and go with the least expensive.

 

[wanrep]

Setting the float height with the needle tip compressed will give you a lower fuel level. That's what I did to get the right level. Mine also dripped a little gas when sitting. Doesn't now.
The part #'s for the pilot jets are:
52...92064-1130
50...92064-1144
48...92064-1143
45...92064-1142

 

[PowerStroke]

If jetting doesn't help, look for an air leak in the cases or even bad reeds.

 

[Racinante]

Hey! Thanks for the Kawi part numbers!!!

Don't you think they would use more of a cronological part number system? I guess that's just to stay mysterious.

I can get pilot jets from Honda-Kawasaki.com for $5.33 each. But, I just found aftermarket jets at my local shop for $4.50 each. Do you think aftermarket would make that much difference? They've got a whole box of anything I would need!

The guy at the shop told me I should go talk to the dealer. He said they might still have bulletins on the proper jetting for my bike. I guess he bought one new in '90 and he went to the dealer and they told him exactly how to jet it!

I'll talk to Kaw tomorrow, and if I have a recomendation from them, then maybe I won't have to buy so many jets. Plus, if I need another one, I can just stop by and pick one up, as opposed to placing a $25 minimum order and waiting at least a week!

Oh yeah! I have an old '75 Yamaha 175 Enduro that I need to check the carb on it. I don't know if it will work, but I might just be able to use the pilot jet out of it! Does anyone know if most jets are compatible?

 

[Racinante]

OK guys!!! Here's the latest.

I've slimmed down from a size 55 on my pilot to a 48. And guess what...
It Idles!!!!! But, it's still way too rich and I just fouled my third plug. This plug only lived in 50 & 48 pilot environment. I think I'm gonna skip 45 & go with a 42 or 40.

The smoke has significantly diminished, but how much should it smoke? Just a lil' from the tailpipe & then it disappears, right? Not look like I've got my afterburners on.

I just wanna say thanks!!!!!! I've spent so much money (well I did need a pipe) chassing what so called "experts" told me. One guy at a small shop charged me $180 just to replace the gear engage spring on the kicker, the water pump gaskets, & clean the carb (which I already told him I did) 5 hours of labor? And it still didn't idle! I don't know about you guys, but I have such bad luck letting anyone else work on my equipment.

But, I do wanna thank you guys! This info was priceless! Hopefully I can "pay it forward!" (If you haven't seen the movie, you gotta check it out)

Thanks Again!!!!

Joe