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Jetting Inconsistencies

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I just had to post what took place last week with my CRF250r. 

 

I rebuilt the carb last week and noticed the last owner of the bike had changed out the pilot jet from a 40 to a 42. A 40 is what the manual calls for at sea level.

 

I'm at 4700 feet so I figured I should at minimum take it back to a 40 due to my elevation. Well, I put the carb back on and could not start the bike for nothin. Thinking I had done something wrong in the rebuild, I ended up requesting the help of the local shop here in town. Long story short-- they ended up putting a 48 pilot jet in and it runs great. Go figure.

 

Just wanted to share so riders understand that you can't always go by the manual. No two bikes are the same.

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This is odd. Are you running a jet kit? Do you have the needle C-clip in the wrong position? Did you change only the pilot jet? Are there any modifications done to the engine? This just seems weird to me as you should be able to do as the manual instructs. 

 

I would still take the bike out for a ride and then read the spark plug as it will tell you if your mixture is correct. You'll know for sure if it's off though if the engine bogs on acceleration (rich) or if the exhaust pops on deceleration (lean).

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This is odd. Are you running a jet kit? Do you have the needle C-clip in the wrong position? Did you change only the pilot jet? Are there any modifications done to the engine? This just seems weird to me as you should be able to do as the manual instructs.

No jet kit. Needle clip is in the correct 3rd position. Yes, only the pilot jet. No mods.

Here's what I'm thinking and correct me if I'm wrong. The bike is in desperate need of a top end (which I'm starting this next week). I'm wondering if the oversized jet was needed to keep it running with the top end being so tired. Your thoughts?

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