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Old 01-01-2004, 11:02 AM   #1
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Question On Carb Needle Settings

I just purchased an XTM 24.7 Pro Pull-Start Engine. I am setting the needles for break-in according to the instructions, hold the throttle barrel open, then proceed to do 3 turns out from fully closed for the high speed needle and 8 turns out from fully closed with the low speed needle.

But I am running into a problem. When I back the low speed neddle out 8 full turns, the low speed needle screw comes out. It is not even in there.

What is a turn? Is it 360 degrees, or 180 degrees? I always thought a turn was 360 degrees, and if that is true, than I don't see how it is possible to back it out 8 turns. It is not a typo either, on the XTM website, the non-pro version of this engine is back out 7 and a half turns from fully closed, so 8 turns is correct.

The high-speed needle on the other hand will back out 3 full 360 degree turns just fine. This is confusing me even more.

Any help is greatly appreciated!
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Old 01-01-2004, 11:44 AM   #2
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The high end needle is used to control total flow rate of fuel. But when engine idling those flow rate of fuel is too much and can't not keep engine idling. So designer use a low end needle to limit those flow rate of fuel. When you half open the throttle,the low end needle will have no effect anymore.

Back to your question,you can try 4 or 5 turns out first. If your engine can't keep idling for a while,lean the low end needle 1/4 turn each time.If your engine is singing when you close the throttle,sometime that means your engine is too lean when throttle closed.So you need to rich your low end needle.

Last edited by dino.tw; 01-01-2004 at 12:18 PM.
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