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CRF450 idle problems

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Hey guys, got a question about my idle on my 450. I just recently purchased a used 2008 crf450r and I am having problems with the idle. Once you crank it up, it idles fine, but once you give it gas and ride for a minute as soon as you let off the gas the idle stays real high for 20 to 30 seconds. I changed the fuel in tank, pulled the carb off and cleaned the carb (it was extremely dirty). Also checked the throttle and it is not sticking. I attempted to adjust the fuel screw and the idle screw with no luck. If this has already been discussed, forgive me, but I couldn't find any post for my exact problem. Any help would be greatly appreciated, thanks.

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your setting the idle with a cold motor, the idle will ramp up as it gets warm. Set the idle once the bike is hot.. You may need to adjust the fuel screw underneath as well, and that has to be adjusted once the bike is hot as well.

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This is the classic "hanging idle" that comes from being too lean (fuel screw/pilot circuit needs to be richened).

Usually a half turn on the fuel screw should take care of this.

I recommend a "flex jet" as this is super handy for adjusting the fuel screw. Also, if the carb was that dirty I would also replace the pilot jet with a new one. Set the fuel screw at 2 turns out to start and you should be golden.

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This is the classic "hanging idle" that comes from being too lean (fuel screw/pilot circuit needs to be richened).

Usually a half turn on the fuel screw should take care of this.

I recommend a "flex jet" as this is super handy for adjusting the fuel screw. Also, if the carb was that dirty I would also replace the pilot jet with a new one. Set the fuel screw at 2 turns out to start and you should be golden.

Too rich can do it too

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Change stock pilot from a 42 to a 48 and it will idle cold as if it was already warm..... And will solve your problems , you will probably need to turn down idle screw sounds like slide stays open too much and adjust your pilot screw, start 2 turns out...

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Hey guys, thanks for the responses to the previous post. Here is what I have discovered after getting the bike warmed up. I can get the bike warmed up and I have the idle screw adjusted to a good idle. However I am still getting a slight hanging idle. I attempted to adjust the fuel screw, but I can screw the fuel screw all the way in and the bike still runs and still has a hanging idle. From what I have gathered, that should not be the case. So my question is, do I need to change the pilot jet and if so what should I get? The bike has an aftermarket R&D bowl and acc. pump. Thanks for any help.

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my bike would hang at times and i never could get the problem figured out but i put a 41 mm carb on it and it does not hang now.i also found if the carb boot is lose it will hang idle high after running hard

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Hey guys, thanks for the responses to the previous post. Here is what I have discovered after getting the bike warmed up. I can get the bike warmed up and I have the idle screw adjusted to a good idle. However I am still getting a slight hanging idle. I attempted to adjust the fuel screw, but I can screw the fuel screw all the way in and the bike still runs and still has a hanging idle. From what I have gathered, that should not be the case. So my question is, do I need to change the pilot jet and if so what should I get? The bike has an aftermarket R&D bowl and acc. pump. Thanks for any help.

If you screw the fuel screw in all the way and your bike continues to run, you need to go down a size or two on your pilot jet. If you go down a size on your pilot jet and you screw the fuel screw in all the way and the motor will not idle and dies, you are in the ball park. Next, open up the fuel screw 2 turns and see how that works.

my 08 crf 450R is cold natured. Does not idle well until it is fully warmed up.

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Another thing you should check is the hot start cable. Make sure it has a little bit of play so it can fully seat. Even the slightest bit open, it would cause a lean condition and make the bike do weird things.

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Thanks for all the advice guys. I just replaced the hot start not too long ago. I will double check it tho when I pull the carb off. I think I'm going to try to go down a pilot jet size.

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If you screw the fuel screw in all the way and your bike continues to run, you need to go down a size or two on your pilot jet. If you go down a size on your pilot jet and you screw the fuel screw in all the way and the motor will not idle and dies, you are in the ball park. Next, open up the fuel screw 2 turns and see how that works.

my 08 crf 450R is cold natured. Does not idle well until it is fully warmed up.

As it should be. :bonk:

There is a "choke" (enricher circuit) for starting it dead cold.

You cant properly jet the thing when its cold. You really shouldnt even try to set the idle until youve run it about 10 mins. around where ever you ride because you want the rads hot, the water hot, the engine heat soaked to proper temp first, otherwise you guarantee it to be too rich.

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Thanks for all the advice guys. I just replaced the hot start not too long ago. I will double check it tho when I pull the carb off. I think I'm going to try to go down a pilot jet size.

I bet your pilot is still dirty. When I service bikes I replace them if they are dirty. Cheap insurance, the orifice is so small that even dirt you cant really see will affect idle.

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