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XR250R carb rebuild

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Hey guys, so I just attempted rebuilding my carb on the xr for the first time and got a rebuild kit & the 135 main and 48 pilot jet, I believe the needle jet was stuck in there because when I put the new one in I couldn't get the needle jet holder (the bit the main jet sits on) to screw in, so I left the new needle jet out assuming the old one is there, also I couldn't find where one of the new o-rings go in the kit I got (I have all the o-rings listed in the service manual installed) also being my first carb rebuild I took the pilot screw out and replaced it with a new one which I probably shouldn't have done, I did all the jets 1 and 3/4 turns out including the pilow screw (starting from bottomed out completely meaning I couldn't screw them in any tighter and 1.3/4 turns out from there, now the issue is even with the bike off as soon as I turn the fuel petcock on the bike starts pissing out fuel from the overflow hose!!! did I do something obviously wrong? when I was doing the throttle valve there was two ways to screw in the link arm, one so it completely covered a hole (I figure its a vent hole and would serve no purpose if I just screwed it in that way) and one where the hole is exposed, but I feel like I am missing something really obvious because how does a bike just start pissing out fuel from the overflow hose after a rebuild if something wasn't missed out not just adjusted wrong :confused::unsure: going over the steps in the service manual I can't find anything I could have done wrong or missed so any help would be appreciated as I can't ride my bike like this :/

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fuel is coming out of the overflow tube because the float needle is not seating properly- could just be stuck, could have debris keeping it from closing all the way. try a light tap on the float bowl with a screwdriver handle to see if you can get it to stop leaking- if not, pull the carb and inspect float needle function and float height. 

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I believe the needle jet is a press fit, not screw in. If it's not damaged or corroded, no reason to replace it.

Did you set the float level? On a 250 I believe it's supposed to be 12.5mm. If it's set too high, or sticking, or the needle valve is hanging up in its bore or it's not seating properly, fuel from the tank won't be shut off properly and it will overflow out of the vent lines.

Did the kit come with a new needle valve? Be sure to check its seat in the carb to be sure its undamaged and corrosion free. You can clean/polish it with a Q-tip.

Sounds like you installed the slide arm wrong. The hole in the bottom of the slide should be left exposed.

Did you replace the oring under the air diverter valve cover(that cover under the choke lever). That may be the oring you had left over.

As long as you got all the parts installed correctly on the new fuel screw, it should be fine. Spring goes on first, then washer, then oring last. Slide that assembly up into the bore. Be sure you dug out the old washer and oring first.

Edited by Trailryder42

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5 hours ago, redhurricane said:

fuel is coming out of the overflow tube because the float needle is not seating properly- could just be stuck, could have debris keeping it from closing all the way. try a light tap on the float bowl with a screwdriver handle to see if you can get it to stop leaking- if not, pull the carb and inspect float needle function and float height. 

as in the float valve? I got a new one in the kit could it be its too small and need to use the old one?

5 hours ago, Trailryder42 said:

I believe the needle jet is a press fit, not screw in. If it's not damaged or corroded, no reason to replace it.

Did you set the float level? On a 250 I believe it's supposed to be 12.5mm. If it's set too high, or sticking, or the needle valve is hanging up in its bore or it's not seating properly, fuel from the tank won't be shut off properly and it will overflow out of the vent lines.

Did the kit come with a new needle valve? Be sure to check its seat in the carb to be sure its undamaged and corrosion free. You can clean/polish it with a Q-tip.

Sounds like you installed the slide arm wrong. The hole in the bottom of the slide should be left exposed.

Did you replace the oring under the air diverter valve cover(that cover under the choke lever). That may be the oring you had left over.

As long as you got all the parts installed correctly on the new fuel screw, it should be fine. Spring goes on first, then washer, then oring last. Slide that assembly up into the bore. Be sure you dug out the old washer and oring first.

Thats right, I wasn't sure how to set the float level as there was nothing wrong with it before so I assumed it wouldn't have any issue, can I do this without that special tool listed in the manual? The fuel valve was sitting in the hole and wasnt down enough to be sitting on that middle lip of the float in the first place so I assumed it can't go down any further and I would have to bend the lip up to get them touching so I just left it.

I left it exposed :) I didn't install the slide arm to cover the hole, you mean the diaphragm one? right next to it? it had a different o ring (a u-ring) which didn't come with the kit so I used the old one as it looks fine I never found the old washer and o ring (I didn't know the screw and those things were in the hole and it all dropped out on the floor during disassembly) but I shined a light into the hole and couldn't find any sign of them or anything to dig for them with.

I did get the bike started in the end after about 50 kicks so I know its working but its just pissing out fuel so it must be over fueling by a lot

Thanks guys

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Watch this tutorial. Shows how to measure and set float height. From your description, you didn't have the carb oriented properly to even gauge if it was ok or not. You do not need the special tool. You can use a set of calipers or a 6 inch scale. If the scale is inch, you can convert to/from metric. 12.5mm = .492 inches

It also shows installation of the slide.

Also shows the Air diverter/cutoff valve.

 

 

Edited by Trailryder42
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Thanks man that video helped a lot, I had another look inside the pilot screw hole and managed to dig up the old o-ring and put the new o-ring, washer, spring and pilot screw in, (could that have been the main cause of the leak?) I also readjusted the float from 14min-25max to about 12.5min-20max, the carb leaked a bit when I first turned the fuel on but after that it seems dry (I will update once I get the intake manifold screw for it and take it for a ride, however I noticed my float is actually chipped a tiny bit on one of the tips

DSC_0028.JPG.7557b0d1d865ff5c72f9fad33273e2f4.JPG

DSC_0029.JPG.9ee5291e27e968e70c53492ac6c31aa5.JPG

Should I replace it or is there any way to fix it? I just bought a rebuild kit and it didn't come with a float and I don't really want to buy an entire rebuild kit just for the float itself.
Cheers guys

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Glad you double checked the fuel screw hole. I bend a small hook in an old guitar string and fish the contents of the hole out with that.

Why are your main and pilot jets not screwed in all the way?

The only thing to worry about with that chipped float is that it isn't a hole. If the float is compromised and it fills with fuel, it won't float properly and fuel level in the bowl won't be correct, most likely too high and cause rich running and fuel venting problems.

Be sure the floats themselves are equal height to each other on their support arm. If they're not, you can set one side to spec and the other will be off.

With the float installed, see how much side to side slop it has on its pin. Also how much twist, as in, cocking one side up and the other side down. A lot of floats I've worked on were excessive. To fix that, I remove the float from the carb, insert its pin and use a pair of pliars to gently squeeze the pins clamping tangs closed just a hair tighter. The pin should still slide in and out freely and the float should pivot on it without any hangups from being too tight. That little tweak makes a big difference in slop when the float is reinstalled and makes float height setting more accurate.

I hate what they've started doing with the new fuel screws. They're supposed to have serrations to make them easier to grab and turn with your fingers but whoever is making these is milling them off.

Did you find where the extra oring you had goes?

Edited by Trailryder42
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7 hours ago, Trailryder42 said:

Glad you double checked the fuel screw hole. I bend a small hook in an old guitar string and fish the contents of the hole out with that.

Why are your main and pilot jets not screwed in all the way?

The only thing to worry about with that chipped float is that it isn't a hole. If the float is compromised and it fills with fuel, it won't float properly and fuel level in the bowl won't be correct, most likely too high and cause rich running and fuel venting problems.

Be sure the floats themselves are equal height to each other on their support arm. If they're not, you can set one side to spec and the other will be off.

With the float installed, see how much side to side slop it has on its pin. Also how much twist, as in, cocking one side up and the other side down. A lot of floats I've worked on were excessive. To fix that, I remove the float from the carb, insert its pin and use a pair of pliars to gently squeeze the pins clamping tangs closed just a hair tighter. The pin should still slide in and out freely and the float should pivot on it without any hangups from being too tight. That little tweak makes a big difference in slop when the float is reinstalled and makes float height setting more accurate.

I hate what they've started doing with the new fuel screws. They're supposed to have serrations to make them easier to grab and turn with your fingers but whoever is making these is milling them off.

Did you find where the extra oring you had goes?

Thats a good idea, I just used the old jet needle, I thought the main and slow jets are meant to be 1 and 3/4 out from bottomed out just like the pilot screw? I might give that a shot when I take it apart.
Didn't even notice the fuel screw was any different :bonk:
Nope still no idea about that o-ring, I am guessing it was meant to be that u-ring that I reused but instead they put an o-ring there.
Cheers

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main and pilot are to be installed all the way- not backed off. ONLY the mixture screw gets backed off from seat by 1.75 turns as a baseline. Be gentle seating that mixture screw, it does not need to be tightened past light seat. you can damage the needle if you get firm with it. 

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2 hours ago, Eryk said:

Thats a good idea, I just used the old jet needle, I thought the main and slow jets are meant to be 1 and 3/4 out from bottomed out just like the pilot screw? I might give that a shot when I take it apart.
 

Where did you get the idea that the main and pilot jets were supposed to be installed like that? Glad you posted the picture and we caught it. If you had left them like that, the bike would have run like crap and they probably would have vibrated out.

Look at this picture. Everything labeled #1 is in the oring replacement kit. Check it against what you replaced and what you didn't to find where that extra oring goes.

XR250 carb orings.JPG

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13 hours ago, redhurricane said:

main and pilot are to be installed all the way- not backed off. ONLY the mixture screw gets backed off from seat by 1.75 turns as a baseline. Be gentle seating that mixture screw, it does not need to be tightened past light seat. you can damage the needle if you get firm with it. 

You are right and that actually saved a big issue down the line as I heard the main jet come off with force when I first started it (I thought it was the float getting unstuck and just today when I took it apart again the main jet was just in the bowl not screwed in, all fixed now, I just do them finger tight with a small socket wrench without using any pressure other than the weight of the wrench when they stop screwing down, lucky :) surprisingly the bike was still running.

11 hours ago, Trailryder42 said:

Where did you get the idea that the main and pilot jets were supposed to be installed like that? Glad you posted the picture and we caught it. If you had left them like that, the bike would have run like crap and they probably would have vibrated out.

Look at this picture. Everything labeled #1 is in the oring replacement kit. Check it against what you replaced and what you didn't to find where that extra oring goes.

XR250 carb orings.JPG

I think it might be the drain bolt (the small one) as I never took that out, or it could be for number 5 but I am 99% sure any o-ring I noticed gone was replaced and there is 0 leaks on the carby right now, I've just taken it apart for the 4th time to screw in the jets and readjust the float to a perfect 12.5mm, as long as there is no leaks there shouldn't be any issues right? This is it:
DSC_0030.JPG.34b5f61dcc8b1bcb64bcd3b2167cbe74.JPG

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I think so, thats the only one I see thats not listed in the manual and has an o-ring in that photo, and it can get changed with the carby on the bike right? I probably won't even bother touching it as I was/am going to be using it as daily transport so I never really drain my carb, bike starts a lot easier now without the choke, think its getting too much fuel as I havent got my modded xr400 spark arrestor pipe yet, any tips on setting the pilot screw without a rev metre? I am guessing by the sound?

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When tuning the fuel screw, I like to start by turning it IN leaner to see if it starts to run worse, to confirm that you can actually lean it too much for the jet that's in it. Then turn the screw out again as the rpms pick up again. Eventually you should get to a point where the idle rpm starts to drop again. That's too rich. Then from that point turn it back in slowly until rpm picks back up again. Right around there is best/highest idle and throttle response off idle "on the rich side". Keep track of how many turns out that is. Always tune with a warmed up engine.

An engine shouldn't start easy cold with no choke. If it does, it's going to be too rich when warm. Indicates pilot jet size it too big(rich). If when tuning the fuel screw, you find best idle and throttle response off idle with the screw 1 turn out or less, that also an indicator that the pilot jet is too big. Going with the next size smaller jet will require you to have to open the fuel screw more, getting you closer to the ideal 2 turns out when you retune it.

Edited by Trailryder42
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