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Why should you not change premix ratio?

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I have a kx250 mixed at 32:1 and it smokes way too much. Why should I not mix it 40:1 without having to change the jets?

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The gas:oil ratio can effect the air/fuel mixture. I believe more oil will lean it out, less oil will richen it up (someone else chime in if im wrong). Ive ran my 01 at 40:1 for years with no issues, with proper jetting. All 2 strokes smoke pretty good until you start riding at speed, some low smoke premix is available as well. Once the bike is warmed up, does it smoke bad while riding?

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The gas:oil ratio can effect the air/fuel mixture. I believe more oil will lean it out, less oil will richen it up (someone else chime in if im wrong). Ive ran my 01 at 40:1 for years with no issues, with proper jetting. All 2 strokes smoke pretty good until you start riding at speed, some low smoke premix is available as well. Once the bike is warmed up, does it smoke bad while riding?

The whole time while riding it

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Is there spooge drooling down the silencer?

Yes, and it's not transmission oil

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Sounds like its jetted rich. When your riding, does it feel sluggish when you wack the throttle wide open?

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Some oils smoke more than others. It may be that. Or you can try the same oil at 50/1 to see what happens, I seriously doubt it will need rejetting. And there is zero chance you will hurt anything with modern oils. But there is one more thing, a KX250 has a few years on it now and you may be having a crank seal issue. Did the smoking just get worse or has it always smoked bad? If it just started it could be the crank seal. Good luck.

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Sure, you can do it.  I am betting that it smokes just as badly.  maintenance,  tuneups,  jetting etc will affect how much it smokes more than the mix ratio.  that said, there are some oils that do smoke more than others.  Most of the name brands have done a good job of making them burn more cleanly.  

If you can't tell me what the float is set at right now,  I think that is where I would start learning a very basic part of how to.  

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Some oils smoke more than others. It may be that. Or you can try the same oil at 50/1 to see what happens, I seriously doubt it will need rejetting. And there is zero chance you will hurt anything with modern oils. But there is one more thing, a KX250 has a few years on it now and you may be having a crank seal issue. Did the smoking just get worse or has it always smoked bad? If it just started it could be the crank seal. Good luck.

It's only has 3 hours on the rebuild and always has the same amount of transmission oil

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Sounds like its jetted rich. When your riding, does it feel sluggish when you wack the throttle wide open?

It runs pretty good other than when full throttle sometimes it doesn't wanna open up completely

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Sure, you can do it.  I am betting that it smokes just as badly.  maintenance,  tuneups,  jetting etc will affect how much it smokes more than the mix ratio.  that said, there are some oils that do smoke more than others.  Most of the name brands have done a good job of making them burn more cleanly.  
If you can't tell me what the float is set at right now,  I think that is where I would start learning a very basic part of how to.  

I'll have to check

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Changing the mix ratio from 32:1 to 40:1 is going to have a minimal effect on smoke or spooge, you need to get the jetting straightened out. That being said with good quality modern 2 stroke oil you should be able to run 40:1 safely.

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By open up completely, if you mean the engine then thats another sign of rich jetting besides the drool. I would grab a new plug or 2 and do a few plug tests/chops. You need the insulator in the plug to be somewhere in between chocloate brown/slightly lighter like a light brown. If its black thats way rich, white is dangerously lean.

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1 minute ago, Yz_Smoker said:


I'll have to check

.  Sad fact of life with carburetors is that the float level RISES as the engine picks up the hours.  That makes it run richer.  People who don't realize that buy different jets,  and that seems to help.  Then it keeps rising and the subsequent owners keep smaller jets.  So while you are in their measuring the float height, take an inventory of the jets which are in there.  If the main jet is more than two sizes smaller than what stock is,  I would set the float,  check the float needle to make sure it is clean and not overly worn.  and reset to factory.  Buying jets is going to be a waste of time before you do that.   

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Another note, as YHGEORGE mentioned, is theres something with the engine thats starting to fail then its useless trying to jet it.

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.  Sad fact of life with carburetors is that the float level RISES as the engine picks up the hours.  That makes it run richer.  People who don't realize that buy different jets,  and that seems to help.  Then it keeps rising and the subsequent owners keep smaller jets.  So while you are in their measuring the float height, take an inventory of the jets which are in there.  If the main jet is more than two sizes smaller than what stock is,  I would set the float,  check the float needle to make sure it is clean and not overly worn.  and reset to factory.  Buying jets is going to be a waste of time before you do that.   

This is dumb question but how do I measure the float height and do the jets have the sizes on them?

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yes,  they have sizes on them (the jets).  For the float,  you will need to get a manual or find one online to get the setting that the factory has in mind.  Then if I am not mistaken there is a good pictorial here on actually setting it.   A small screwdriver is all you need once you have the carburetor out and sitting upside down on a table or bench.  Once you set it, you can blow through the fuel line while you work the float up and down to make sure that the float shuts off where you set it.  if it doesn't it can be from the rubber being worn on the spring loaded tip have a tired spring.  it is fast and free if the parts are still good.   

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yes,  they have sizes on them (the jets).  For the float,  you will need to get a manual or find one online to get the setting that the factory has in mind.  Then if I am not mistaken there is a good pictorial here on actually setting it.   A small screwdriver is all you need once you have the carburetor out and sitting upside down on a table or bench.  Once you set it, you can blow through the fuel line while you work the float up and down to make sure that the float shuts off where you set it.  if it doesn't it can be from the rubber being worn on the spring loaded tip have a tired spring.  it is fast and free if the parts are still good.   

I will take it apart soon probably Friday

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I have found that any time I am going to do something with small parts that I do it when I have some time to give it.  You can get a pretty good parts schematic of your carburetor, which is probably a 38mm Keihin pwk.   Most of those set at 16 mm.  way easier to describe once you have pictures.  anyway,  bikebandit.com would have the parts diagram.  

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