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fcr jetting time? surging / backfire help

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have finally got the drz400e i bought rebuilt (bought it with stuffed crank) its stock with the fcr39mm carb,it has snorkel removed and some small holes in side cover for more air, when crusing at 50kmh or so in 3rd mayb 4th to it seems to surge or run as if its out of gas chugging sort of it goes good under heavy acceleration and what not, also does a loud backfire sometimes after a heavy deceleration. i am unsure of what jetting and needle clip it has as i cant get hold of seller, does anyone know if the carb may be the cause and if so what jets and stuff i should have at sea level with a stock exhaust that i think has been  hollowed out a bit as it is loud, thanks

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If it's just surging in the mid-range and runs fine under hard acceleration, just try moving the needle clip down one groove to raise the needle a bit, that may be all it will take.

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stock needle position is 4th groove from top.  in that position the bike is able to run without big issues.

leave it at 4th clip and try to discover the real problem.

possibile causes of lean mixture at very small throttle positions: clogged or too small pilot jet , root diameter of the needle too small, fuel screw missing or not dialed.

imho  you should take it apart and check the size of every jet and needle. i discovered that some owners detune their carb installing jets without any knowledge.

Edited by 30x26
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thanks for replys just got carb off today,  needle was on pos 4 i moved to 5 main jet is 165 should this be changed to a 160? first time doing all of this

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thanks for replys just got carb off today,  needle was on pos 4 i moved to 5 main jet is 165 should this be changed to a 160? first time doing all of this

 

Yes...It doesn't require a 165 mj

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