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Old Apr 27, 2011, 05:08 PM
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ronbo422's Avatar
USA, TX, Leander
Joined Dec 2006
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OS .61SF Needle setting?

Hey guys,
I'm putting my 2 nitro planes back in the air after 8+ years in the "hangar". Both are equipped with OS .61 SF's. What should my initial needle setting be? I started one today and it idles great and runs good up to about 1/2 throttle, but when I go WOT it dies. Seems like it's rich but I turned needle in 3 clicks and it does the same. I wanna make sure I'm starting with the right setting but can't find my original paperwork from OS.

Thanks,
Ronbo
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Old Apr 27, 2011, 09:03 PM
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downunder's Avatar
Adelaide, South Australia
Joined Sep 2003
3,058 Posts
An engine that's quite rich at full throttle will be running in a 4 stroke mode with lots of smoke from the exhaust. If yours doesn't get that 4 stroking sound after 1/2 throttle before cutting out then it's likely too lean on the high speed needle. Open the needle 1 turn and try again.
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Old Apr 27, 2011, 09:23 PM
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1320fastback's Avatar
USA, CA, Oceanside
Joined Jul 2008
3,264 Posts
Mine likes to run at 1 and 3/8ths turn from closed.

I believe most OS engines are less than 2 turns out for the final tune, 3 turns out has to be slobbery.

What carb do you have?
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Old Apr 28, 2011, 02:30 AM
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Letchworth, Great Britain (UK)
Joined Jul 2004
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I would suggest that if it starts okay, then your "initial" needle setting is fine. Provided the carburretor is clean, and the jets are not bunged up with waxy varnish from the old fuel, you should be able to then tune it at WOT (or close to) by turning the main needle until the revs peak, and then open it a couple of clicks to make sure it's not running too lean.

If you're finding that turning the needle significantly (we're talking quarter-turns here, not clicks) doesn't make any difference, then you may have an air leak somewhere in the system, or the carburretor is partially blocked with hardened fuel.
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Old Apr 28, 2011, 10:40 AM
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pryor808's Avatar
United States, NY, Medford
Joined Oct 2008
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Start off at 2 1/2 turns out.
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Old Apr 28, 2011, 03:32 PM
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ronbo422's Avatar
USA, TX, Leander
Joined Dec 2006
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Thanks. I'll give it a shot this weekend and see how it tunes out.

~Ronbo
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Old May 01, 2011, 11:29 PM
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DGrant's Avatar
United States, CA, Clovis
Joined Mar 2004
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2 1/2 turns is about right to get any engine started... and that's all you need initially is to be in the ballpark... if that doesnt work try 3 turns.... if that doesn't work.. try 2 turns.... you just need too get it ticking over enough to fine tune it.

Once you get it running... open throttle... if it dies immediately with no sputter whatsoever.... its lean... turn out your needle about 1/4 turn...try again.... once you get it to transition to full throttle and running... turn your needle.. whichever way you've been turning.. listen for the peak RPM's... when it hits its absolute peak... turn out your needle about 1/8 of a turn(richen).... thats a ballpark to actually fly... this is all generally speaking... as it might take longer to do the first few times you try it... and you might find a quicker way... but essentially this is starting/tuning a 2stroke in short form. Good luck.
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