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April 01, 2020, 12:48:21 pm

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Low end needle on a SC 120FS

Started by Ronos, March 11, 2018, 09:39:49 am

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Ronos

Hi all, a question, I have a SC 120 FS Glow 4stroke,how far does the LEN screw in? I want to find the default setting by blowing in a tube, but the LEN when screwed in seems to have no stopping spot. With the barrel fully open, you can see the part of the needle with the rubber O ring when the LEN is screwed in, I haven't gone any further in case it screws out, and I don't want to take it apart to recover the LEN.

Brian Cooper

This is not a definitive way to acquire the exact settings but it will give a good starting point. In any case, the settings will be different for different fuels.

Open the main needle one full turn.
Close the throttle so that there is (just) no hole showing.
Attach a piece of fuel tubing to the main fuel feed nipped on the carb.
Screw the low end needle in whilst SUCKING on the fuel tube. . Like sucking through a straw.
When you (just) can't draw any air, it is done.

Start it up and adjust the tuning on the top end and then adjust the low end.
Have fun.

B.C.

Ronos

March 11, 2018, 19:30:38 pm #2 Last Edit: March 11, 2018, 19:32:09 pm by Ronos
Thanks Brian, I suppose it the reverse way of finding a starting point, sucking instead of blowing. I will give it a go and see what happens. But is there a stopping spot for the low end needle or dose the needle just screw out  if you go to far?

Brian Cooper

Yeah, if you keep unscrewing it, it will come out.
When an engine has done a lot of service, sometimes the threads on the low end needle can become a bit slack and the needle can move by itself with engine vibration.   A tiny drop of thin cyano (on the end of a pin) wicked into the thread will keep it secured.

B.C.

Ronos

Once again, thanks Brian I'll bear that in mind 👍