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01 WR250F Hanging Idle

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I bought an 01 WR250F at the beginning of the summer.  It ran well when I bought it, I rode it a few times, then I decided I would take the carb apart just to clean things out and inspect for any seals/gaskets that may need replaced.  I found the A.P. pump diaphragm was deteriorated and the bowl gasket was also worn.  I replaced these and put it back together.  This is where my problems began.

 

When I would start the bike, it would only run with the choke on.  I pulled the carb and replaced the pilot jet with a brand new 42, installed a JD Jet Kit with 185 main and blue needle, fifth clip from top.  Fuel screw was ~ 2 turns out.  I sprayed carb cleaner through all the passages and didn't notice any clogs.  I reinstalled carb, found that it would idle fine but when I would turn the throttle, the revs would climb normally, but then would not return to idle when the throttle was closed.  I removed carb again, found a few small cracks in boot between carb and motor, I replaced the boot with new one and new clamps.  I removed the throttle slide assembly and inspected the o-ring on the slide halves and it looked fine.  I reinstalled the carb, and had the exact same problem.  I turned fuel screw in then out and the problem didn't change.  I tried revving the bike by disconnecting the throttle cables and turning the input linkage by hand.  The revs would still hang after I released the throttle.  I checked all of the vent tubes and didn't find any clogs.  I sprayed WD-40 at all the boot connections and around the hot start plunger and didn't notice any air leaks.  I noticed the carb throat was pretty wet with fuel when I took it back apart, but I'm not sure if it was necesarilly any more than normal. 

 

If anyone could shed any light on this issue, I'd appreciate it.

Edited by YZF429

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Do you know the condition of the intake valves?

A lot of fuel in the intake tract might indicate a leaking intake valve or a tight valve... spitting back up stream a little.

Is the valve clearance in spec?

 

If you have had the head off recently, did you check valve sealing by spraying brake cleaner or carb cleaner into the intake side and exhaust side to see if there was any seeping past the valves?  That's how I check mine before I install the head.

 

Also, just a comment on your description of the JD kit.

Pilot jet may be a little rich with a 42, but 2.5 turns out on the fuel screw is reasonable for that jet.

A 185 main jet sounds rich. Blue needle sounds correct, but the clip in the 5th from top sounds like you have it pulled up way too high.

Most of the time JD recommends the 3rd from the top.

 

Only other thing might be a leaking hot start plunger... might check that...

Good luck

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Carb cleaner on an fcr carb is a big no no. You could have swelled the diaphragm on the slide plate, or ruined the internal gaskets in what is called the "death chamber" id suggest what Ron did first but if you can't trace it down you may have damaged the carb seals they are replaceable I believe JD jetting sells the mid body gasket.

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Do you know the condition of the intake valves?

A lot of fuel in the intake tract might indicate a leaking intake valve or a tight valve... spitting back up stream a little.

Is the valve clearance in spec?

 

If you have had the head off recently, did you check valve sealing by spraying brake cleaner or carb cleaner into the intake side and exhaust side to see if there was any seeping past the valves?  That's how I check mine before I install the head.

 

Also, just a comment on your description of the JD kit.

Pilot jet may be a little rich with a 42, but 2.5 turns out on the fuel screw is reasonable for that jet.

A 185 main jet sounds rich. Blue needle sounds correct, but the clip in the 5th from top sounds like you have it pulled up way too high.

Most of the time JD recommends the 3rd from the top.

 

Only other thing might be a leaking hot start plunger... might check that...

Good luck

I haven't checked the valves yet as it was running/starting fine.  I was going to check them over the winter.  I haven't had the head off.

 

I moved the needle up to the third from top clip and installed a 180 main jet and still have the same problem.  I've inspected the hot start plunger and didn't see anything out of the ordinary.  I also sprayed around it with WD-40 and didn't notice a jump in idle.

 

Carb cleaner on an fcr carb is a big no no. You could have swelled the diaphragm on the slide plate, or ruined the internal gaskets in what is called the "death chamber" id suggest what Ron did first but if you can't trace it down you may have damaged the carb seals they are replaceable I believe JD jetting sells the mid body gasket

 

I've taken apart and inspected the slide plate/diaphragm and it looks fine.  There is some wear on the plate but nothing that looks unusual.  I haven't had the carb halves apart, I suppose I could have damaged the gasket.

 

 

When I rev the bike, it sounds almost like the throttle plate is not returning to closed.  The engine RPM just drop slightly and then stay at a higher than idle RPM.  The throttle plate snaps back closed forcefully, like it should without the bike running, and it appears to go fully closed when I watch the cable linkage when it is running. 

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Dude, if that's the carb I think it is, and there is a middle body piece between the throttle slide and the bowl, then you don't need to take that part off.  I've read horror stories about that.

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Dude, if that's the carb I think it is, and there is a middle body piece between the throttle slide and the bowl, then you don't need to take that part off. I've read horror stories about that.

That is the carb had a buddy trash one dipping it in carb cleaner had to reseal the death chamber with new gaskets that are hard to come by

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I'm betting your Throttle position sensor is out of adjustment, maybe you moved it when you removed the carburetor.  Anyways this is a common cause of hanging idle.  Mark the position of the tps and adjust it one direction and see if this cures the problem.  There is also a way to check the TPS voltage in the repair manual and on youtube.

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