I have a OS 46fx that I have ran for a while with no problems. The last time out I noticed it was slugish form idle to WOT. The low end was rich. I adjusted the mixture screw in to lean it out and restarted the engine, and the screw turned back to where it was.[X(] The screw is so loose that it is just turning be itself with the vibration.[:@] How do I fix this?

Is this the high speed needle? If so, isn't there a detent "spring" that applies pressure to the detents on the main needle valve screw head? (the knurled part that you turn with your fingers.. that metal thing that presses against it).

If you do have one of those, and you should, you can carefully bend it so that it makes good contact with the detents or knurles on the finger-twisting part of the HS needle valve.

CGr.

You can try wraping telfon tape around the LSN's thread. Makesure you wrap it in the correct direction.

Or you can add a drop of CA or BLUE loctite after you set it. it'll last for a little while.

Replace the LSN 'O' ring

CG it is the LSN that is lose. the one with the spring around it. would it heip to replace the spring?

Thats the idle stop screw, not the low speed neecle valve. The LSN is inside the throttle barrel and you can only see the sloted head.

John

Ok. Is that screw supossed to be that lose. This makes since why it wasn't leaning out Is there a default setting for the idle stop screw and what is that screw for? Is mine ok being that loose? Now I gotta find a screwdriver small enough to reach the LSN

This should be your carb http://www.osengines.com/parts/ev15460aa.pdf
As you can see item #6 and it's spring are the idle stop screw. It's used to set the absolute low end of the throttle and NOTHING to do with mixture.
Item #2 is the idle mixture screw and can only be seen from the exhaust side of the engine and is VERY close to the prop so do not attempt to adjust while running.

It shouldn't move while running. If you can run it in further without making it so the engine won't idle down then do so. Otherwise maybe stretch the spring slightly so it will apply slightly more pressure/resistance.

That's the idle stop screw.lol ...if it's the FX...okay.

You can tighten it more if the barrel still closes. Make use the barral can move freely
It'll vibrate out. Use Blue loctite or CA it. I've double nut it before.
It's there more as s retainer to keep the barrel in place not so much as an idle setting for aircraft models.

For cars it acts as an idle setting...because there's breaks on those things.

The idle stop screw serve two functions, the end rides in a concentric grove machined into the barrel and this moves the barrell in and out as it opens and closes. the second function is to stop the barrel from fully closeing and makeing this adjustable. The normal procedure is to back this screw out so that the barrel will fully close and we can control idle cutoff from the Tx. If you back off to far the barrel can come out. Before you do this remove the screw and stretch the spring and replace.

The LSN is within the barrel just like the drawing. Close the throttle so barrel it is fully closed and screw the LSN in til will go no more. Now back the LSN out three full 360 turns and this will almost make the screw close to flush with the barrel face. This will be your new starting point. On this carb you lean the low range by screwing that screw in no more than about an eight turn each time.

John

Thanks for all your help. Once I found the right screw It just needed a 1/4 turn and its perfect. thanks again.

Love it when a plan comes together.