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2008 popping in mid

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I have a 2008 with a new big bore installed. Bike has a new head with all new valves. I set valve clearance at .006 in, and .012 ex. I checked clearance at 4 hrs. and they haven't moved. ( Del West in.) Bike has 45 slow jet, 178 main jet. Bike is really strong running, but when holding rpms steady at 4000 to 7500 and not accelerating bike will pop slightly and like it is very lean.  I've tried a 48 slow jet, then added  180 main no difference. I've opened the pilot from 1 turn out to 3 turns out, no difference.  bike starts one kick, and idles nicely. I'm in Az., and it does not over heat even with the big bore.

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I went to a larger main with no difference for more fuel. I also used a larger slow jet for more fuel with no difference. Raising the needle will give me fuel sooner, but not more. 

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1 hour ago, jack13 said:

I went to a larger main with no difference for more fuel. I also used a larger slow jet for more fuel with no difference. Raising the needle will give me fuel sooner, but not more. 

Why would you replace the main or pilot jet with a larger one when you said its happening mid throttle????? Guessing is the worst thing you can do, Do as HRC said and lower the clip one position and retry it and see if it helps your problem! 

Edited by ThrustWasher
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I just try the needle clip and it made no difference. I watch that video serval times. Thank you for your solutions. I've never had a problem with  carb setting up before.  Also it only  is happening at about 1/8 throttle, just barely cracked open, not when under load. Thanks again.

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Correct, if you accelerate to 4500 rpm, you will then need to back off of throttle to stay at that speed, you will find you will need only a small amount of throttle position to maintain this rpm, provided you're not climbing a grade. You are almost coasting, very little gas needed. If you go to a higher rpm you will again need to back off the throttle to maintain this new speed. Your rpms are not match to an exact throttle opening, nor is your speed. Open the throttle, speed up, bring throttle back to maintain the desired rpm or speed. Same as your car, you don't need full pedal to go maintain 70 mph. Again thank you for your response.

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Correct, if you accelerate to 4500 rpm, you will then need to back off of throttle to stay at that speed, you will find you will need only a small amount of throttle position to maintain this rpm, provided you're not climbing a grade. You are almost coasting, very little gas needed. 

Depends entirely on what gear your in, when i accelerate i keep accelerating until i need to get on the brakes. I ride my crf450r either on the gas or on the brakes, its a race bike meant for racing not coasting.

 

 

 

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I do the same hence the big bore kit, but I also like my bike to be as perfect in every gear as I can. I'm old and will take the time to make it correct. It was working perfect before, and I will figure this out. Maybe a crack in the carb body on the side after the slide. Wouldn't be the first time. Again thank you for your ideals.

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I do the same hence the big bore kit, but I also like my bike to be as perfect in every gear as I can. I'm old and will take the time to make it correct. It was working perfect before, and I will figure this out. Maybe a crack in the carb body on the side after the slide. Wouldn't be the first time. Again thank you for your ideals.

You also be a air leak at the boots of the carb body.

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Along with mostly new parts the air boot is new , and the vacuum seal in carb. What is confusing me is the motor ran perfect for first 1 1/2 hrs. I checked the air boot using wd40 while the motor was running. Change jets one at a time. It also has new air screw with O rings. When I took out the old air screw the top O ring was split, and I thought this was my problem, but it still has the small popping when the throttle is slightly opened at the 4000 to 7500 rpm range. Below  4000 rpm it's ok, above 7500 engine is pulling enough that it has no popping. I filled around the air screw with a small amount silicone. I will look at carb body next for maybe a small crack. I'm grasping for straws now.

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