kx 125

[brendon]

i've just got a mint kx 125 91 model. it smokes a little and leaves a black wet oil stain on the back mudgaurd. is my pre mix wrong @100ml to 5 litres of fuel or is it something else. please help as i'm new to moto x.

[mustangfury]

hey,  I have a 1993 kx 125 and I am having the same problem.  If you view my forum Oil spitting exhaust, you will see some of my questions and findings.  They may be helpful to you.  What spark plug are you using?  I know some oil dripping is normal because it is a two stroke.  The mixture you are using is actually a little thin if my calculations were correct you are using about a 50:1 ratio.  50 parts fuel, one part oil.  The manual for the kx 125's recommends a 32:1 mixture.  Your ration should be ok.  I usually run mine between 40:1 and 32:1.  Running yours at 50:1 puts less oil in the fuel then what is recommended which will cause the top end to wear faster due to less lubrication and will need rebuilding more often.  50:1 is about the lowest I would go but you should be alright with that.  I also wouldn't go any higher, not even the slightest bit, than 32:1 because it commonly causes engine bogging and less performance depending on the fuel you use.  If you are using pump fuel use at least 93 octane.  I am still experimenting with mine and i am going to try using a hotter plug to hopefully burn off some of the extra oil.  Mine also spits oil at the connection from the big pipe to the silencer pipe.  A BR9 series plug will work good for your bike.  Also check the spark plug and see if it is like a burnt brown.  If it is black and gunky you are getting oil build up on it.  This can be caused by a lot of things so let us know what you find with the plug, what type it is, and we'll try to help.  Sorry for rambling on but you said your new to riding so i tried to give a lot of the basics.

Good luck

[brendon]

thanks for your help. all this info's great, just what i need. the plug im using is ngk br10eg.
the plug itself is a brown/black colour and very wet.
all info greatly appreciated

[Hillclimb#42]

I agree with mustangfury. I see that its very wet, but it shouldn't be. It should be carmel brown on most of the electrode. 50:1 is probably ok, in my opinion, as long as you are riding with it screamin' most of the time. With a 125, you probably are. 32:1 - 44:1 is what I would use, if you ride in tight trails or ride easy. Make sure you use a good 2-stroke oil, high octane gas, and once you establish what gets the plug brown, stick to that exact equasion. If you feel that you are on track with the preliminaries, lean out the mixture screw. (counter-clockwise) about a half turn.
 You can check jets in carb, needle adjustment, and mixture screw recommendations on the jetting chart on here. Also it is important to look at the altitude and temperatures local to you when using that chart. What works in the summer, will need adjusted in the winter. Cold weather leans the mixture due to the denser air. High altitude and/ or warm weather fattens up the mixture, so you have to correct by leaning out the screw adjustment.
 Float height is also critical to performance. If you are bouncing around alot a lower float height may be needed, which also was brought up on here somewhere.
 Worst case scenario, if its blue and stinkin smoke, you may be ready for a bottom end rebuild.
Check out the related threads on jetting for pages and pages of ideas. Its all on here. Keep feeding us symptoms. We all like to fix the kaws.

[mustangfury]

"Worst case scenario, if its blue and stinkin smoke, you may be ready for a bottom end rebuild." - Hill climb #42

My 1993 kx 125 has blue smoke come out of the exhaust until it warms up is this normal or does that mean a bottom end rebuild is comming up?  Should there be smoke comming out of the pipe? and what does it mean if it is blue, black, white?  Just curious for future reference.

What is involved with a bottom end rebuild?  Just taking it apart and replacing the gaskets if nothing is broken?  or is there something broken/worn if there is smoke of a certain color?

Thanks.  Didn't think I was going to be the one possibly getting help in this forum

Thanks again

[Hillclimb#42]

Smoke is really no big deal, as long as its two stroke oil. If it starts burnin' crankcase oil, it is really no big deal either, until you know what else that means. What I'm trying to say is, its not likely that you are all the sudden gonna be burnin all of the crankcase oil from the bottom end, but it plays havoc with your jetting. It gives you rich symptoms, even though the jetting is correct. It could also pull air in, which is also bad for mixture.
 I think you may just have a typical fat mixture while choking her to get it fired, if it stops. My bikes both smoke alot, until warm. They smoke less with better gas and perfect jetting. The best way to tell is the smell. A good two-stroke oil smells like you're at a race, but but if it starts being a lingering burnt plastic funky smell, then its the seals.
  The school of thought is that it all depends on time on the bike, as to how often to rebuild. I agree with a few exceptions. If a bike sits too long it can be as bad or worse than a bike that gets rode on a regular basis.
 In hillclimbing, I think people are rebuilding top-ends in the winter only. Of course the real fast guys do it twice a year. If you just ride for fun, I say a bike can go 3-5 years between rebuilds. Many guys will disagree probably, but once you get it right, it will haul for a long time.
 Rebuilding the top-end is fairly simple, and manageable with a helper, but bottom ends require splitting the cases, that requires a special tool.  When you get to the point that you want to do a full rebuild, it really pays to have it all done by someone who does it all the time. You probably need to go through it all at that point.
 Replating the cylinder, all new bearrings, several seals, and a expert's eye can get you several years of reliable riding time.
 Ok, I'm rambling on, Black smoke would be excess fuel. It would probably be barely running if itwas doing that.
White smoke would be water, which is way bad. Head gasket, or something worse like broken water jackets.
Blue Smoke, funky smellin blue smoke, could mean oil seals.
 Winter is coming up, keep an eye on it, and be prepared if it needs it.

[mustangfury]

Thanks.  Very Helpful.