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Discussion Starter · #1 ·
Hello all,
I recently purchased a very nice 1990 lt250s quadsport. It ran fine for a few weeks then it stopped idling well. I had a local guy adjust the valves. I rebuilt the carb, set the float and cleaned everything well. I have cleaned out the fuel tank and installed a new throttle cable. The needle is set on the 3rd notch. It will start but won’t idle/ stay running. Any suggestions. The idle screw and pilot screw don’t seem to have any effect on the idle. Thanks in advance!
 

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2000 King Quad 300 4x4 1987 Quadrunner 250 4x4
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Hello all,
I recently purchased a very nice 1990 lt250s quadsport. It ran fine for a few weeks then it stopped idling well. I had a local guy adjust the valves. I rebuilt the carb, set the float and cleaned everything well. I have cleaned out the fuel tank and installed a new throttle cable. The needle is set on the 3rd notch. It will start but won’t idle/ stay running. Any suggestions. The idle screw and pilot screw don’t seem to have any effect on the idle. Thanks in advance!
Do you know if you put the lines in the right spot on the carb and is the petcock still good? And do you know if it's getting to much fuel which would make it stall out because it's getting to much fuel and not enough air or to little fuel which would give to much air and not enough fuel making it stall out also. The other problem might be the fuel pump which might need cleaned. From what I know, the fuel pump should be located around the front left kinda tucked under the fender some. I've had a 1987 ltf250r 4x4 and it's been sitting for years and the carb badly needed cleaned and so did the fuel pump, and check the fuel lines too.
Hope this helps!
 

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Discussion Starter · #3 ·
Do you know if you put the lines in the right spot on the carb and is the petcock still good? And do you know if it's getting to much fuel which would make it stall out because it's getting to much fuel and not enough air or to little fuel which would give to much air and not enough fuel making it stall out also. The other problem might be the fuel pump which might need cleaned. From what I know, the fuel pump should be located around the front left kinda tucked under the fender some. I've had a 1987 ltf250r 4x4 and it's been sitting for years and the carb badly needed cleaned and so did the fuel pump, and check the fuel lines too.
Hope this helps!
I changed the petcock because it was leaking. It doesn’t have a fuel pump. The fuel line goes from the petcock straight into the carb. It doesn’t stall when you give it gas, just won’t idle. I’m confused as to why the pilot and idle screws seem to have no effect on the idle speed.
 

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2000 King Quad 300 4x4 1987 Quadrunner 250 4x4
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I changed the petcock because it was leaking. It doesn’t have a fuel pump. The fuel line goes from the petcock straight into the carb. It doesn’t stall when you give it gas, just won’t idle. I’m confused as to why the pilot and idle screws seem to have no effect on the idle speed.
Is it the original carb or a knock-off? And when you can get it started, does it smoke at all? If so what color is the smoke.
 

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But there might be a screw on the side of the carb that adjusts the idle.
 

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Discussion Starter · #6 ·
Is it the original carb or a knock-off? And when you can get it started, does it smoke at all? If so what color is the smoke.
It is the original mikuni carb. It doesn’t smoke at all. The idle screw seems to have no effect on idle speed
 

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It is the original mikuni carb. It doesn’t smoke at all. The idle screw seems to have no effect on idle speed
I'm not completely sure about this, but maybe the threads are stripped and that's why it doesn't have any effect on it. If so you may have to get a completely new carb instead of a rebuild. And the jetting might be to small for it's idle speed or to big? I'm pretty stumped on this, if the carb was cleaned, the valves were adjusted, and it has a new petcock. The only thing I can think of now is the timing may be off but if it was off then it'd be smoking, but it's not.
 

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First thought for me is the fuel pump is removed and gas straight to carb. Make sure you turn the fuel off when not using. And if the fuel is leaking around the needle valve in the bowl adding more gasoline into the stream. It's getting gas from somewhere. The high end needle valve may need to be dropped so it closes the hole in the jet completely.
Hey kinda spitballing here. If it was mine I'd put it back to oem. These fuel systems are finicky
 

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First thought for me is the fuel pump is removed and gas straight to carb. Make sure you turn the fuel off when not using. And if the fuel is leaking around the needle valve in the bowl adding more gasoline into the stream. It's getting gas from somewhere. The high end needle valve may need to be dropped so it closes the hole in the jet completely.
Hey kinda spitballing here. If it was mine I'd put it back to oem. These fuel systems are finicky
Yeah, one of the o-rings might be bad and it's leaking gas through that way. That would make a lot of sense.
 

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2000 King Quad 300 4x4 1987 Quadrunner 250 4x4
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If anyone knows where I can get a new carb, please let me know.
Search up "1990 Suzuki LT250s Carburetor" and see which one you'd like, just be careful of the cheap ones, they tend to be chinese knock offs and may not fit your quad right, or it might need new jetting, or it may just not work. And the ones up the in $100+ range seems to be the ones that would work almost straight out of the box with almost no issues. I'd do your research on each carb you check out to make sure it's one that will work for your quad.
 

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Discussion Starter · #12 ·
Search up "1990 Suzuki LT250s Carburetor" and see which one you'd like, just be careful of the cheap ones, they tend to be chinese knock offs and may not fit your quad right, or it might need new jetting, or it may just not work. And the ones up the in $100+ range seems to be the ones that would work almost straight out of the box with almost no issues. I'd do your research on each carb you check out to make sure it's one that will work for your quad.
So I searched up what you suggested and I found that summit racing sells mikuni carbs. Question is, my research Has yielded different results. I have seen where the 250 s runs a vm 26 and I’ve also seen vm 34. Which is the correct one?
thanks for all your help
 

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So I searched up what you suggested and I found that summit racing sells mikuni carbs. Question is, my research Has yielded different results. I have seen where the 250 s runs a vm 26 and I’ve also seen vm 34. Which is the correct one?
thanks for all your help
Hm, I checked the compatibility on both of them and they both said they weren't combatable? The best I could suggest is going to your quad and taking the carb off and measuring where it goes into the engine and go from there. Thats the best I can think of right this second, I'll so more research just incase.
 

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I believe the VM26 has a cable going to the slide, the VM34 cable controls the plate, slide is vacuum powered. Is your carb flat on top or does the throttle cable go in there? Check the intake boot for cracks, mine was pretty bad, making it not idle properly.
 

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Hello all,
I recently purchased a very nice 1990 lt250s quadsport. It ran fine for a few weeks then it stopped idling well. I had a local guy adjust the valves. I rebuilt the carb, set the float and cleaned everything well. I have cleaned out the fuel tank and installed a new throttle cable. The needle is set on the 3rd notch. It will start but won’t idle/ stay running. Any suggestions. The idle screw and pilot screw don’t seem to have any effect on the idle. Thanks in advance!
Carburation simplified 1. Pilot system -idle to 1/8-1/4 throttle. 2, Needle -1/4 to 3/4 throttle 3. Main jet 3/4 to full throttle. If your idle mixture screw is on the engine side of the carb it controls gas, If it's on the intake side of the carb it controls air. If your low speed mixture screw has no effect then it is obvious that the pilot system has blockage. The one thing about "rebuilding" the carb is that most times it's not needed. The pilot system is blocked either with debris or varnish from old gas. The pilot passages are extremely small on a carb of your size. You have to force cleaner through the passages and make sure that it sprays from every pilot orifice. As an example on a 500 sportsman a wire from a wire brush was to large to clean the pilot jet. For you since it ran well then suddenly had issues it sounds like a piece of dirt got in and blocked you pilot.
 

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Carburation simplified 1. Pilot system -idle to 1/8-1/4 throttle. 2, Needle -1/4 to 3/4 throttle 3. Main jet 3/4 to full throttle. If your idle mixture screw is on the engine side of the carb it controls gas, If it's on the intake side of the carb it controls air. If your low speed mixture screw has no effect then it is obvious that the pilot system has blockage. The one thing about "rebuilding" the carb is that most times it's not needed. The pilot system is blocked either with debris or varnish from old gas. The pilot passages are extremely small on a carb of your size. You have to force cleaner through the passages and make sure that it sprays from every pilot orifice. As an example on a 500 sportsman a wire from a wire brush was to large to clean the pilot jet. For you since it ran well then suddenly had issues it sounds like a piece of dirt got in and blocked you pilot.
And this is where I let the full on experts take over 😂
 

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Discussion Starter · #17 ·
And this is where I let the full on experts take over 😂
So I removed the carb again today and completely stripped it down and cleaned everything with a pick and brush set along with 2 cans of carb cleaner. I reinstalled it. I was able to get it to idle by adjusting the throttle cable quite a way out. The mixture and idle screw still have no effect. Now when I increase the throttle, it idles pretty high for about 10 seconds and then returns to lower idle. Now it does seem to be blowing some white smoke though. I’m totally confused
 

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Discussion Starter · #18 ·
So I removed the carb again today and completely stripped it down and cleaned everything with a pick and brush set along with 2 cans of carb cleaner. I reinstalled it. I was able to get it to idle by adjusting the throttle cable quite a way out. The mixture and idle screw still have no effect. Now when I increase the throttle, it idles pretty high for about 10 seconds and then returns to lower idle. Now it does seem to be blowing some white smoke though. I’m totally confused
Also, I have found a few new replacement carbs for the lt230 quadsport, but none for the 250. Can the 230 carb be used and maybe just change the jets?
 

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So I removed the carb again today and completely stripped it down and cleaned everything with a pick and brush set along with 2 cans of carb cleaner. I reinstalled it. I was able to get it to idle by adjusting the throttle cable quite a way out. The mixture and idle screw still have no effect. Now when I increase the throttle, it idles pretty high for about 10 seconds and then returns to lower idle. Now it does seem to be blowing some white smoke though. I’m totally confused
Hm, the white smoke means that there's some sort of water vapor in the cylinder or exhausts and it's burning off. This may also be a resolute of a lot of water in your gas, hense why it's white smoke and why it won't idle and the throttle has to be increased so much for it to idle.
 
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