YZF250 overheating while idling on stand

[drudin]

well, it's cold in TN now and even though I'm not riding every week, I try to start the bikes often to keep them in shape.

But strange things are afoot! My 2003 YZF250 has been reluctant to start (normally not a problem). It has recently gotten an oil and oil filter change,and a clean air filter. I replaced the spark plug and got her running. I left it idling on the stand about 5 minutes and when I returned coolant was streaming out the overflow. I've never had coolant overflow before.

Yesterday I started the bike again. Once again it didn't want to start. Acted like it wasn't getting a spark so I took off the coil and cleaned the contact to the plug and got it started again. Left it for 5 minutes and heard the idle jump up. when I went to see what was up... you guessed it, coolant gushing out the overflow.

I'm a newbie rider (2 years now) and new to wrenching on bikes. I'm fairly competent mechanically but this has me wondering. The problem starting just happened after my last moto practice and the bike ran fine at practice.

any advice would be great

Drudin

 

[biglou]

Have you richened up the pilot circuit? Larger pilot jet and/or backed the pilot screw out some? It's my understanding that thumpers will run hotter if lean. I've started and reved, but never left idling for 5 minutes, my 426 in all kinds of temps and never had an overheating condition. Are you sure you have the correct amount of oil in the motor? Low oil would contribute to this as well. For help starting, turn the idle up a bit, blip the throttle a couple times before kicking, too.

 

[Rich Rohrich]

You can't let any of the new four-strokes sit and idle for 5 minutes without causing overheating problems. Once the radiators are hot to the touch you should either ride it or shut it off.

 

[drudin]

thanks BigLou.
you may be on to something about the jetting. I neglected to mention that my float got stuck open last practice (I asume I knocked a little junk loose when cleaning the air box) and had to open the carb at the track. although I was careful, maybe I messed up the main jet possition some. I did remove the jet to make sure it wasn't clogged. I'll check in the manual about resetting the jet. Pretty sure about the amount of oil but will double check.

Any other opinions?
Dan

 

[drudin]

Rich;
oh.
That would about cover it then! thanks.
dan

 

[Yogurt]

Yea Rich nailed it on the head. Even if your bike was jetted perfectly, no MX bikes like to stay idleling long while stationary. In order for them to cool efficiently air must be passing through the radiator. 2-strokes get hot, but 4-strokes get even more hot, because of the additional moving parts.