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I have a 2009 crf230f that I recently bought. It starts great other than being cold natured. When idling it will be fine then it will blow air back through carb and into air box. You can hear this happen and fill the air come out of the top of air box. This causes the bike to lose rpm's and will eventually kill the engine. Can someone please tell me what is causing this? Intake valve issue, carb adjustment or other? Thanks

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Thanks for the feedback. I adjusted the valves this afternoon and found the exhaust was right on but the intake you could only get .0015 under. I adjusted it to .004. Started bike and still have the backfire through carb problem. It also seems to backfire through exhaust on deceleration worst than before I adjusted valves. Any advice would be greatly appreciated. 

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Just now, Dale Crabtree said:

Jetting is stock 102 and 42.5. Exhaust baffle out intake baffle still in.

You need a 120 main

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Your getting a lean decel popping. Your bike probably runs hotter than it should. As for back pressure, following this thread to see 

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As long as the intake resitrictor is in you will be lean but not dangerously lean.  The backfiring/popping is likely due to the 42 pilot.  Most like a 45 and some, like mine, need a 48.

Start with a 45 pilot and 120 main, exhaust baffle in or out, and see if that improves the issue.

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What is the intake restrictor and how do I remove it? The air mixture screw is also shaped like a D so I haven't been able to adjust it. I ordered a bit to fit it also. 

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11 hours ago, Dale Crabtree said:

What is the intake restrictor and how do I remove it? The air mixture screw is also shaped like a D so I haven't been able to adjust it. I ordered a bit to fit it also. 

Put your finger in there and give it a good pull.  I replaced my 2009 screw with a 2003-3005 screw.

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12 hours ago, VortecCPI said:

Put your finger in there and give it a good pull.  

LOL, I still don't know what your talking about here??? Edit, are you talking about the top of the air box rubber piece? 

Edited by 1gr8bldr

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13 hours ago, VortecCPI said:

Put your finger in there and give it a good pull.  

Geez.... If I had a nickel for every time I've heard that.... 

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LOL, I still don't know what your talking about here??? Edit, are you talking about the top of the air box rubber piece? 


Yes remove the seat first, it right under the seat.

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Just now, adnohguy said:

 


Yes remove the seat first, it right under the seat.

 

Never heard it called a "restrictor"

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Always heard "air box mod". LOL, I thought he may be referring to the metal screen behind the filter.... LOL, until he said reach in and pull

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Never heard it called a "restrictor"



Correct me if I'm wrong but technically it was put there by the factory to quiet air intake noise.

It works very well as a noise restrictor. (Because it restricts air flow)

Two strokes with a very open air box make a lot of air intake roar when they are WFO.

RD 350~400, Banchee's, H1, H2, TRX 250r all good examples of that.

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I removed the carb today and cleaned it. Installed new 45 slow and 120 main and problem is gone. Bike starts right up even when cold and idles perfect. Have not rode the bike yet to check throughout the rpm range. Also have the air/fuel screw 2 full turns out. Would removing the air box restrictor help more? Thank for everyone help. 

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