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Help with YZ250F running lean

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We've been through the carburetor 3 times, the last time by a qualified mechanic. Inspected and cleaned everything, set all jets and adjustments to spec. The end result every time is the bike won't run without the choke unless the idle is cranked way up - which then results in backfiring, hesitation, etc. We've even tried moving the clip to position 5 and turning out the pilot screw, neither of which seemed to help.

Engine is good, no cracks in the intake boot, new filter, no exhaust leaks, can't find anything dirty or clogged within the carb or vaccuum leaks anywhere. :thumbsup:

Anybody have any other ideas or experience a similar situation? Do we need to make more drastic adjustments or start changing jet sizes? It has been about 40 degrees here during the day and I know these carbs can be sensitive, but trying to get some input before buying new parts to throw at the problem.

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Vacuum release plate is installed upsaide down. Square edge should be to the bottom.

No, installed correctly - good thinking though.

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well you havent said what jets are in the carb.

and since you have not said what year bike, i dont know what carb you really have on it.

yes there are differences.

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No, installed correctly - good thinking though.

With a hole visible on the bottom.

Your symptoms sound just like the plate upside down.

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Hot start works properly?

Pilot jet is new?

If it is not a slide problem, either no fuel is flowing in the pilot circuit, requiring the slide to be up high enough to 'be on the needle' or the hot start is passing air, leaning the idle mix too much.

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yeah def check the PAJ and PJ circuit, like someone already said, to get the bike to run youre basically having to start the bike "on the needle" meaning youve eliminated your pilot circuit from injecting gas into the engine....try going a little richer on the PJ and making sure you're PAJ is squeeky clean...

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well you havent said what jets are in the carb.

And since you have not said what year bike, i dont know what carb you really have on it.

Yes there are differences.

2005 yz250f

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Hot start works properly?

Pilot jet is new?

If it is not a slide problem, either no fuel is flowing in the pilot circuit, requiring the slide to be up high enough to 'be on the needle' or the hot start is passing air, leaning the idle mix too much.

PJ was not new, but picked up another 42 and a 45 yesterday. Hot start works seems to work properly. Will replace the pilot and see how that goes.

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Another thing to look at is to see if the hot start plunger is fully seating in the carb. A worn out/hard to engage hotstart cable will not allow the plunger to spring back into position.

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Another thing to look at is to see if the hot start plunger is fully seating in the carb. A worn out/hard to engage hotstart cable will not allow the plunger to spring back into position.

HS plunger and spring seems to work fine when removed. How would you test whether it is seating properly?

From earlier, jets are stock. 42 Pilot / 182 Main

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have you removed the o-ring out of the fuel screw circuit yet?

might take a magnifing glass to see that it has been shoved up inside.

it is very evident your PJ circuit is plugged. compressed air probably will NOT remove a piece of o-ring in the fuel screw circuit. unless you blow it from the front side.

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