Fix my coil problem with a rubber hammer. The seal kit I bought must have had a o-ring that was a little larger than normal. Now I have another problem.

After complete rebuilt the bike started right up but after 5 minutes steam comes out of the radiator cap and fluid comes out of the overflow tube. The temperature of the fluid really isn't hot.

I have another 2009 KX250f, (the rebuild is my son's race bike), and took off the radiator cap and used it with the same problem.

This bike was a basket case that I basically rebuilt from scratch and it starts right up and sounds strong but after 5 minutes, I get overflow.

Any ideas?

 

Welcome, lash. My kneejerk diagnosis is a head gasket. Have you checked compression and/or are you sure mating surfaces were flat upon the rebuild? No cracks or integrity issues? Use the proper head gasket goo (or not; depending upon type of gasket)? I'm no expert, but that's where I'd begin.

 

i have the same problem with my 07 kx250f . steal is coming from the bottom of my rad, but i think its from spilling a bit of fluid on the frame (idiot move) ......but i have other concerns.......the bike was always babied, maintained very well.....and yesterday i started her up for the first time in 2 months, winter here in toronto (n) and she didnt want to idle with choke pushed in.....run amazing with choke pulled out.....also, my exhaust header (Aftermarket FMF Powerbomb) has a cherry type glow on it......that heat cant be good for an engine lol.

 

If the header is glowing you've been revving the snot out of it. Stop! Revving a bike in neutral is useless for checking the tuning and only causes unnecessary wear on the machine. Worst case you can over rev it and drop a valve, slightly less (but not unusual to see both) is causing ring flutter and scoring the bores. There is nothing good that can come from abusing the engine like that.

If it wont idle when warm it's time to clean out the carb.

 

I concur! lol (from some movie I watched recently)

but I do agree with the reasoning.

 

Did research on the web and found that it is a common thing. The last race we were at i looked down the starting gate and every 250 there was overflowing. The radiator needs air flow to cool. Also, everyone recommended to upgrade the cap with a higher pressure release and that it would allow the motor to run cooler. Did that and have not had any problems. Some of the pictures on the web the pipes look like they were going to melt. I have a pro circuit pipe which is thin wall titanium which after thinking about it, I should be concerned if it did not glow red.

 

I hate late starting grids. I do not run a fan on the 10r, and if the starting grid is delayed, these puppies get hot! That is why you see the riders shaking their arms in the air and what not when a start is delayed and you are stuck on the grid.

 

agreed, it seems like a lot of people who have these idling problems are starting their bikes in cold weather, i took mine out after an 8 minute warm up and did not notice any problems, exhaust was nice and idling with choke pushed in was fine.......problem starts when the bike is cold and its idling for a long period of time.....then as soon as you push choke back in it bogs out, or simply dies. like another member stated, 4 strokes need airflow to cool down temps in exhaust and no issues at idle. my opinion is dont even start your bike in the winter, when riding season starts just a fresh complete fluid change and your set to go!