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A couple questions on my '06 KX250f

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Hi all. I finally made the switch to the 4-stroke side and I'm a bit confused by how my new bike is acting. Keep in mind that I'm a first time four-stroke owner with little knowledge on carb tuning in general. Firstly, when I bought the bike it ran well, with a bit of throttle hesitation. Immediately after purchasing, I changed the oil (Motul 10w-40 synthetic) and oil filter (OEM Kawi filter). Also I cleaned air filter, drained the gas, all that good stuff that one should do after buying a pre-owned bike. I'm also pretty sure the valves need to be shimmed, but I couldn't swear on it. I then deep cleaned the bike with a pressure washer (I'm not proud to say that I did not use a exhaust plug  :banghead:  ). Bike is also bone-stock with what appears to be fairly low hours, judging by the low wear on the entire motorcycle.

 

Enough back-story. The problems now are:

  • the bike spits out white-ish smoke (doesn't appear to be leaking coolant; I've checked the coolant levels periodically and they haven't dropped.
  • when I rev (in neutral), the bike revs great, but when I release the throttle, the bike idles very high and stays that way until I kill the engine.

If anyone could offer some help, it would be incredibly appreciated  :thumbsup: Thanks guys!

Also, any general 4-stroke maintenance tips are welcome!

Edited by weaverwacker

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Hi all. I finally made the switch to the 4-stroke side and I'm a bit confused by how my new bike is acting. Keep in mind that I'm a first time four-stroke owner with little knowledge on carb tuning in general. Firstly, when I bought the bike it ran well, with a bit of throttle hesitation. Immediately after purchasing, I changed the oil (Motul 10w-40 synthetic) and oil filter (OEM Kawi filter). Also I cleaned air filter, drained the gas, all that good stuff that one should do after buying a pre-owned bike. I'm also pretty sure the valves need to be shimmed, but I couldn't swear on it. I then deep cleaned the bike with a pressure washer (I'm not proud to say that I did not use a exhaust plug  :banghead:  ). Bike is also bone-stock with what appears to be fairly low hours, judging by the low wear on the entire motorcycle.

 

Enough back-story. The problems now are:

  • the bike spits out white-ish smoke (doesn't appear to be leaking coolant; I've checked the coolant levels periodically and they haven't dropped.
  • when I rev (in neutral), the bike revs great, but when I release the throttle, the bike idles very high and stays that way until I kill the engine.

If anyone could offer some help, it would be incredibly appreciated  :thumbsup: Thanks guys!

Also, any general 4-stroke maintenance tips are welcome!

I would go through the carb and make sure all the jets are clean. Make sure you have the correct air/fuel mix.  The smoke might not be a problem. If its a thin white smoke you could always be running rich.  A thick white smoke could be a problem but its a bit harder to diagnose. If you said that its not the coolant then im not 100% sure.  If you have the ability to, i would take off the head and check out the pistons, rings and gaskets. As long as its not blue, i wouldnt be TOO worried. The revving part is most likely the carb.  If you clean out the carb and there is still that problem, go ahead and order JD jet kit (if you want to spend the money) I heard that bumping up the pilot to a #42 helps.  I order the jet kit and it was amazing

As for tips (not maintenance) When starting the bike when its really hot on a hot day, pull the hot start level in and give it some light kicks.  Not even from the top, just to get some fresh air in there.  You'll soon start to feel it kinda "grab" And want to turn over, thats when you go from the top and give it a nice kick. Then let go of the hot start level

That reminds me, make sure your hot start isnt stuck :) 

Cheers!

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I have a how to video on valve adjustment:

 

 

 

The bike revs high because it is lean. Here is a fuel screw adjustment procedure:

 

 

 

I also have videos on a complete top and bottom rebuild for this bike. I also jetted it and and the throttle response is amazing now:

 

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