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Hanging / high idle causes - help needed!


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I went with a friend of mine to look at and ultimately purchase a used 2007 CRF50 last week.  While originally checking it out, I noticed that the idle would hang a bit after letting off the throttle (basically after the throttle is open and then closed, the engine will stay at a high RPM and not settle back down to normal idle for different amounts of times - sometimes just a few moments, other times up to 8-10 seconds), I figured it would be something minor like the throttle cable or gummed up carb, so I told him it was good and he bought it.  I took it to my house to go over it and see if I could figure the issue out, but have been unsuccessful.  I changed the oil, spark plug and filter (the filter and interior of the air box were pretty sopping wet with oil when I first opened it up).  I also took the carb apart and rebuilt it fully with an all balls kit.  None of this changed the mannerisms that I described above.  I checked the cable and it seems fine, I also could actually see the slide opening and closing with the throttle tube in the carb.  I've been told that this issue might be due to an air leak after the carb.  I sprayed carb cleaner all over the intake in an attempt to find a leak, but I wasn't sure if I did.  There were a few times that I sprayed and the idle hopped up, other times it didn't.  I did set the fuel/air screw and idle screw at the factory setting after the rebuild as well.

I feel bad because I went to look at the bike with my buddy and told him it was good, and now I can't get it straightened out for him.  Any help or suggestions would be much appreciated.  I can give a better description or put a video up of it if that would help.  Thanks!

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See if it does better with a partial choke on. This would mean that it's to lean. Not likely, but you could rule that out. A worn out needle jet would do the same, but not likely. A missing o ring on the air screw. An intake leak. Very rich idle jet. EDIT, I just googled it. Does yours have a pressed in idle jet?

Edited by 1gr8bldr
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Brackmant,

First thing, I wouldn't be freely spraying carb cleaner all over. It will eat away any rubber or plastic you spray it on. Especially the foam of an air filter. 

I use carb cleaner to clean the metal parts of the carb itself, but when it comes to anything else, I'll use brake cleaner. Even to test for air leaks.

Our 50 had the same problem with idling down. It's been so long since it's been ridden, I don't remember if we got that cleared up or not. Guess I should check. I assumed it was the throttle cable needing lubed, which I should probably do as well since I haven't 

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  • 1 month later...
I went with a friend of mine to look at and ultimately purchase a used 2007 CRF50 last week.  While originally checking it out, I noticed that the idle would hang a bit after letting off the throttle (basically after the throttle is open and then closed, the engine will stay at a high RPM and not settle back down to normal idle for different amounts of times - sometimes just a few moments, other times up to 8-10 seconds), I figured it would be something minor like the throttle cable or gummed up carb, so I told him it was good and he bought it.  I took it to my house to go over it and see if I could figure the issue out, but have been unsuccessful.  I changed the oil, spark plug and filter (the filter and interior of the air box were pretty sopping wet with oil when I first opened it up).  I also took the carb apart and rebuilt it fully with an all balls kit.  None of this changed the mannerisms that I described above.  I checked the cable and it seems fine, I also could actually see the slide opening and closing with the throttle tube in the carb.  I've been told that this issue might be due to an air leak after the carb.  I sprayed carb cleaner all over the intake in an attempt to find a leak, but I wasn't sure if I did.  There were a few times that I sprayed and the idle hopped up, other times it didn't.  I did set the fuel/air screw and idle screw at the factory setting after the rebuild as well.
I feel bad because I went to look at the bike with my buddy and told him it was good, and now I can't get it straightened out for him.  Any help or suggestions would be much appreciated.  I can give a better description or put a video up of it if that would help.  Thanks!

Replace carb and be done
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  • 3 weeks later...

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