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New Hot Starting Problem with FI bike . . . Any Ideas Welcome . . .

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Bike is a 2011 KX250F with the 2012 ECU and dual injectors.  Already swapped the plug.  Bike starts as normal cold.  Bike has always started like never wanted to quit, hot or cold, until recently.  There are three variables (changes) since it ran perfectly, but two of them don't make sense as the cause the problem, so maybe you can school me on this.

 

Variable #1:  The oil seemed low before a race, so I added Kawi Synthetic 10w-40 to regular 10w-40 to top it off.  I figured the blend wouldn't make a bit of difference.  I also figured the over-fill situation I caused would not be a problem.  It was probably 150 ml overfilled.

 

Variable #2:  I put a 2014 stock exhaust system on it because I figured the expansion chamber might do something good.  Not sure if this would cause any kind of starting issue.  Would not make sense to me, but maybe . . . 

 

Variable #3:  The bike recently had new valves installed and ran perfectly for 15-20 hours.  Recent check shows intakes are where I set them, but exhaust valves are looser.  My guess is carbon build up on the exhaust taking down compression so warm starts are an issue.  Timing is good.

 

My plan is to pull the head to inspect the valves and confirm, but if either of the first two variables could have contributed, I would be interested to hear your thoughts.

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Bike is a 2011 KX250F with the 2012 ECU and dual injectors. Already swapped the plug. Bike starts as normal cold. Bike has always started like never wanted to quit, hot or cold, until recently. There are three variables (changes) since it ran perfectly, but two of them don't make sense as the cause the problem, so maybe you can school me on this.

Variable #1: The oil seemed low before a race, so I added Kawi Synthetic 10w-40 to regular 10w-40 to top it off. I figured the blend wouldn't make a bit of difference. I also figured the over-fill situation I caused would not be a problem. It was probably 150 ml overfilled.

Variable #2: I put a 2014 stock exhaust system on it because I figured the expansion chamber might do something good. Not sure if this would cause any kind of starting issue. Would not make sense to me, but maybe . . .

Variable #3: The bike recently had new valves installed and ran perfectly for 15-20 hours. Recent check shows intakes are where I set them, but exhaust valves are looser. My guess is carbon build up on the exhaust taking down compression so warm starts are an issue. Timing is good.

My plan is to pull the head to inspect the valves and confirm, but if either of the first two variables could have contributed, I would be interested to hear your thoughts.

intake or exhaust valves leaking down

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I would go with something to do with the exhaust valves, the first 2 wont make any difference to starting.

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intake or exhaust valves leaking down

 

 

I would go with something to do with the exhaust valves, the first 2 wont make any difference to starting.

 

Thanks to both of you.  I agree.  I pulled the head and found leaky exhaust valves.  Obviously loose because of carbon build-up.  Re-cut seats, cleaned 'em up and will re-shim.  Hope that does it.  As always, I appreciate your feedback.  :thumbsup:  :thumbsup:

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intake or exhaust valves leaking down

 

 

I would go with something to do with the exhaust valves, the first 2 wont make any difference to starting.

Just to close the loop, problem solved.  No question the leaky exhaust valves made all the difference.

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