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2004 Crf 250x smokes in start up runs fine till it gets hot then dies

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Hello, I have a 2004 crf 250x that smokes when I start it.  After riding it for about 4 minutes it starts running weird then dies. It quits revving up and looks like it has black smoke coming from the exhaust before it dies.  The only known problem with it is that the battery is shot.  I’m not a mechanic by any means but could use some help.

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Is the smoke on initial start up black (rich) or blue (burning oil) ?

 

The black smoke when riding would indicate a severely rich condition, 

I'd start by checking/adjusting the carburetor's float level and making sure the fuel inlet needle and seat are in good condition/properly sealing.

 

Edited by mlatour

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When it starts I’d say the smoke is a white ish blue.  I just adjusted the air fuel screw and noticed on the carb their was a overflow pipe missing. I sprayed some carb cleaner in the hole and put a new iver flow pipe on it and it seems to be working fine now.  I’m not sure why  or if the carb cleaner fixed it but it seems to be running right now

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A bit of blue (oil) smoke during initial start-up may be a sign of leak valve seals.

If more whiteish, keep an eye on your coolant's level.

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No, just means if the circumstances are right (engine stopped with the leaky seal's valve in the open position)

some oil can run down the valve stem and, puddle in the port or, run down into the combustion chamber/sit on top of the piston

until the engine is fired up again and it burns off.

 

Edited by mlatour

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I think it might be a problem involving coolant I just road it for a while and then turned the fuel petcock off and let it run out of gas then when it shut off their was coolant bubbling and going into the overflow

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If you let a warm / hot liquid cooled 4-stroke idle at a standstill (very bad habit) for more than 30 second or until it runs out of gas, 

getting hot enough to overflow the radiator is to be expected.

Do that too many times and you might blow a head gasket or warp the mating surfaces.

 

Edited by mlatour

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