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Carb needle help


Guest Elmo
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After completely stripping my very cheap lexmoto xtr 125 and replacing upgrading what I could (swing arm,forks,bearings etc). I have no mechanical knowledge really but I have a eidetic memory so putting back together was easy really, my question is on the carb needle there is a small circlip? And several small grooves which said clip fits into, what would be the effect of moving this clip from the bottom groove to the top as there is about 10 mm difference? Cheers in advance

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The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle. The jet needle is a long tapered rod that controls how much fuel can be drawn into the carburetor venturi. The thinner the taper, the richer the mixture. The thicker the taper, the leaner the mixture since the thicker taper will not allow as much fuel into the venturi as a leaner one. The tapers are designed very precisely to give different mixtures at different throttle openings. Jet needles have grooves cut into the top. A clip goes into one of these grooves and holds it from falling or moving from the slide. The clip position can be changed to make an engine run richer or leaner, If the engine needs to run leaner, the clip would be moved higher. This will drop the needle farther down into the needle jet and cause less fuel to flow past it. If the clip is lowered, the jet needle is raised and the mixture will be richer.

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Cheers stu, now I understand what it does. One more question, I've noticed that when I roll on the throttle about an eighth of it full travel I get what I can only describe as a dead spot where the revs die, could this be a problem with said needle?

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The difference is not having any throttle at all.lol ,I recently stripped my carb,needle back in and pressed the throttle grip and it was just playing and wasn't pulling the cable. after some fiddling I discovered that if you don't get the grooves inside the barrel right then the spring surrounding the needle will be compressed a lot hence no throttle. that 10mm will compress the spring just enough to give the correct throttle response(if not put in right then it's pretty much fully compressed like when it's on full throttle)


Hope I understood you question correctly and what I said makes sense,good luck 8-)

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