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Excess smoke on KX250

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Rode a couple of weekends back and it rode pretty well. Recently did a top and bottom end and wanted to start the jetting process after getting a few hrs. on the motor (the bike is relatively new to me and has had a bog). A couple of days ago I set the float height to the recommended 6.5mm +/- 1 mm. The bike fired up and ran no problem.

The issue that came up is it now smokes A LOT more. It smokes a little from idle and more beyond idle. When I grab some throttle and let off, a plume of smoke rolls out the silencer and takes a second to calm down.

I've since been into the carb a few more times verifying the float level, I dropped the pilot 1 size, put it back and lowered the float level 2mm all in an attempt to see what's up.

I can't find any debris in the carb. The jets are all new. On the Float needle I can barely see the area the needle has been contacting the seat but there is no ridge at all.

Heres a quick vid I took this morning.

Any thoughts/ideas are greatly appreciated as I'm at a loss.

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sounds like you crankshaft seal might be shot it will suck oil from your transmission check that first drain the tranny put the correct oil in it and ride when you have ridden a while drain and measure the oil it will tell you real fast if this is your problem the tough part is on the last kx250 i rebuilt i had to split the cases to replace the oil seal

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after watching the video it looks like you have either added way too much oil to the gas or have it jetted too rich or the oil seal is bad another way to tell is pressure check the motor if the motor wont hold pressure it is most likely the seal.who put it together it should of had all new seals and the person should of pressure tested it

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I did the motor work. It was my first one and I did not pressure test. (didn't think of it) I installed every new seal that came with the top and bottom end kit.

I thought this morning that maybe I brain farted and got my mix ratio wrong but the 2 problems I see is the smoke and it seems to be chugging fuel all of a sudden.

I thought of the crank seal but it doesn't seem to be using any trans fluid. It seems odd that if it is the seals it didn't smoke like this from the get go. I've heard to test the crank seal with soapy water (looking for bubbles) into the trans breather so I'll give that a shot today or tomorrow.

This one definitely would require the cases to be split to change the seals. :busted:

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Why change the seals if your transmission fluid isn't low? It could be that your jetting is just off. You've just tightened up the motor considerably. Try leaning out air screw, pilot, needle jet, and main jet in that order. One circuit at a time.

Your coolant remains stable too?

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The coolant was my first thought when this started and that hasn't dropped a bit. I've let the motor fully cool before checking and it remains at the same level.

The carb currently has a JD kit in there with their primary recommendations. I wouldn't think it would smoke this bad on those settings but I could be wrong.

I'm going to avoid the seals if I can but I'll do the soapy water thing and go from there.

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Just ran it and sprayed soapy water on the trans. breather and it would slowly form a 1/2" bubble. Any thoughts what that means regarding my seals?

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pressure check the motor and see what you get.if it is not using transmission fluid then i doubt it is the seal also i would think the transmission would build a little pressure they do have a breather on them i think it has been so long i cant remember.what pilot jets and main jets are in the bike you should be running stock jets even with a pipe i do not think the jet size should change putting to big of a jet will make it smoke also what does the air filter look like if it is over oiled or restricted the bike will pull more fuel from the carb

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The Filter looks good. Cleaned it during the motor work and it still looks great. It was well wrung out before I put it back in so I'm guessing there isn't too much oil in it.

The jetting in the carb is to the specs of the JD Jet kit for this bike with stock settings. I think the pilot is a 45.

Haven't had a chance to pressure test. I'll try to do that in the next couple of days.

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what main jet is in the bike? also did you have the same jet kit in the bike before you rebuilt the bike? how many turns is the mixture screw out? does it smoke this bad when you are riding fast? it sure sounds like it is either too rich in the carb or the seal is leaking sucking oil from the tranny and a small seal leak will make it smoke but not suck a lot of tranny oil.also if the choke on the carb is sticking i am not sure is it is a enricher circut it will have the same effect

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I believe it currently has a 158 main. The air screw is 1.5 out (I've adjusted it in and out for high idle). When I start the bike with the choke and I kill the choke, there is a distinct change in the motor. I'm believe this to mean the choke is function correctly.

Before tearing into the motor to change the crank seals, is there any other way to check or to verify that it is the definitely the crank seals?

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i would not tear in to the motor unless i had too.buy a pressure tester they are around a hundred dollars and pressure test the motor that is a lot less headache than tearing the motor down for nothing.also when you are running wide open is it like a mosquito sprayer? if it runs ok and just smokes a little i would run it.the mixture could be wrong if it pressure checks ok i would lean to the carb an air leak makes a 2 cycle run lean and what mixture is your fuel 32;1 and what kind of oil do you use

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I run 32:1 with Motul full synthetic. I haven't had a chance to run it hard just yet. Hopefully on Saturday I'll be able to.

Is the pressure tester you're talking about a compression tester or something else?

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the leak down tester is just as it says a leak down tester it hooks up to a air compressor and it has one or 2 gauges and it screws in to the spark plug hole you have to block off the exhaust and the intake it comes with rubber plugs or you can buy them at the hardware store like the ones they use on car blocks the temp. rubber freeze plugs. most engine builders for 2 cycle engines pressure test the motors because if you have an air leak on the 2 cycle it will lean it out causing seizure or oil to be sucked out of the tranny if it is the right crank seal

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Thanks for that link. I'll have to see if I can whip that up and test this weekend.

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