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07 KX250F carb base settings

By stevensj13,
in KX250F/X

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stevensj13

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Alright guys, I need some help. Can anyone tell me what the base settings on a KX250F carburetor would be? I downloaded the service manual but couldn't find it, neither in the carburetor section or the fuels system specs section. Just wondering if anyone knew where the screws are set at the factory so I can go from there. I'd be chasing my tail if I put the screw at 1.5 turns out and the base setting was 3 turns out. Let me know, thanks

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stevensj13

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Typical starting point for a fuel screw is 1.5. Get the bike running, fine adjust for a perfect strong idle. Done.

 

The fuel screw should never be opened more than 2.5 turns.

Fuel screw is for idle only.

Awesome, exactly what I needed to know. The bike will start after some coaxing, it revs out great but it won't idle for sh*t. The carb is spotless, I'll adjust the fuel screw and see if I can get it tuned out. I'd like to have the bike ready for a ride this week. 

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stevensj13

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If the fuel screw does not seem to have the desired effect, you'll want to try a BRAND NEW pilot jet (#42) and also confirm all the parts of the fuel screw (spring/washer/oring) are intact.

 

 

Haven't been able to get it to keep a solid/consistent idle. Sometimes it idles at 2800-3000, rev it a few times, then it'll just stall when you aren't revving it. Then it'll idle high. Dunno, strange. Revs out clean, no popping on decel, pulls strong. The inside of the carb is spotless, all the jets are clean. It has a remote fuel screw, can't remember the name. A friend of mine installed it when he owned the bike before me and he runs a bike shop, and rode this bike, and knows what hes doing so I trust that. The bike did idle when it was put into storage in winter of 2013, but the carb is clean as a whistle. One thing I've noticed, the throttle slider is very slightly loose in the bore. it slaps around when you tap it from the back or front. It doesn't shake around or anything, but if you tap it with your finger you can tell its got a tiny bit of play and does make a tapping noise. The return spring is right. I haven't taken the top cover of the carb off (where it says "CR"). Other than that, the old hot start cable nut (plastic) stripped out and I replaced it with one of the aftermarket aluminum ones, with a fresh new O ring. Should seal fine. I also checked and yes, the hot start plunger is moving and free. 

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stevensj13

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You need a BRAND NEW pilot jet. Still

 

Why would I need a new pilot jet if the one thats in it has no oxidization, looks new, and is perfectly clean? Genuinely wondering, not trying to sound like a smartass. I'm not too familiar with these newer 4 stroke carbs with accelerator pumps and all that, maybe theres something I'm missing. 

 

If you didnt remove the top of the carb how can it be spotless ?

 

The slide will eventually wear and the slide plate also , slide plate can be replaced as well as the slide plate seal when worn  

 

I removed the float bowl and all the jets/float/needle. It looked like a brand new carb. I spraying thru every passage anyway to be sure. I didn't pull the top off the carb because i assumed that had to do with the throttle slider and linkage, which all seemed to be working (other than a tad loose in the bore) and I'm pretty sure fuel/air don't flow thru the throttle linkage area of the carburetor under that top cap. I could be wrong, like I said I'm not super familiar with these newer carbs. I'll look into the sides/slide plate and see what they cost. 

 

Side note, went for a ride today thru the trails. the bike runs mint at low RPM, crawls thru trails no problem, pulls hard and strong with no breaking up all the way to full throttle, and its starting to run a bit longer when you pull in the clutch, IE idle a tad before it stalls. The bike didn't get too hot, its not blowing black smoke. It just seems to be an idle issue. It also can be a bitch to start once its warm though, but it will start.

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William1

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For a bike to idle, the alow air jet, passage ways, pilot jet and fuel screw must all be good. You tell us the passage ways are clean, that the fuel screw is good, you did not remove the slide, so we have assume it is good. 99.9% of the time, the remaining issue is the pilot. Many people tell us the '...the pilot looks fgreat...' until they replace it and find out it was the trouble. It is a $5 part and popping in a fresh one confirms/denys that is a problem. But it usually is.

 

Humor us, put in a brand new pilot jet. Then do the fuel screw/pilot setup/

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the fuel screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle knob to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly).  Once warmed, slow the idle speed (knob) to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the fuel screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,850 rpm, but go by the spec in your manual.

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