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Crazy high revs on startup, dies when choke turned off

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Hey all,

Let me preface by saying I've rebuilt a few motors but I'm by no means a professional

I have a crf50 motor that will start up first kick but revs like CRAZY and if the choke is off it won't run at all. I took the thing apart and the cyl wasn't bad nor the piston I put new caskets everywhere on the top end and put it back together. It has solid compression, after all it runs like a banshee when you start it. I cleaned the carb really really well and have a few times at this point. The valves are adjusted perfectly and everything is timed right. I've tried just about every combination of settings with the carb. 

The one thing I did notice was that there was a good amount of carbon on the valves. I also took apart the carb once and the gas in there was dirty and brown and the main jet was clogged. 

Is it possible that if the intake valve isn't closing all the way that could cause this?

thanks in advance for the help

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It sounds like the classic case of the non-removable pilot jet being clogged, you have to use a wire strand from a wire brush, or a torch tip cleaner to get clean, along with carb or contact cleaner and lots of compressed air. Make sure you spray cleaner through the two holes in the back of the carb where the airbox or filter attaches, to backflush through the main and pilot jet passageways. It also sounds as if you may have installed the throttle slide backwards in the carb throat. The slightly beveled edge of the slide goes to the back (airbox or filter) end of the carb

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14 hours ago, dirtbkr188 said:

It sounds like the classic case of the non-removable pilot jet being clogged, you have to use a wire strand from a wire brush, or a torch tip cleaner to get clean, along with carb or contact cleaner and lots of compressed air. Make sure you spray cleaner through the two holes in the back of the carb where the airbox or filter attaches, to backflush through the main and pilot jet passageways. It also sounds as if you may have installed the throttle slide backwards in the carb throat. The slightly beveled edge of the slide goes to the back (airbox or filter) end of the carb

Thanks for the tip, I'll try those methods today. I know what you mean about the slide going in wrong and although I had done that previously it is installed correctly now.

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On ‎5‎/‎24‎/‎2017 at 1:48 PM, dirtbkr188 said:

It sounds like the classic case of the non-removable pilot jet being clogged, you have to use a wire strand from a wire brush, or a torch tip cleaner to get clean, along with carb or contact cleaner and lots of compressed air. Make sure you spray cleaner through the two holes in the back of the carb where the airbox or filter attaches, to backflush through the main and pilot jet passageways. It also sounds as if you may have installed the throttle slide backwards in the carb throat. The slightly beveled edge of the slide goes to the back (airbox or filter) end of the carb

+1 on the above. All I can add would be, Choke lever down is off, Choke lever up is on. It is definitely a carb problem.

Good luck

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