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OS FS40 4 Stroke

Old 07-19-2007, 04:57 PM
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Default OS FS40 4 Stroke

I received a old 40 4 stroke recently that was all gummed up. I worked it loose, reset the valves at .003, cleaned the carb reset the air bleed with a pin & set the needle open at 2 turns. I got it running using 15% nitro & 18% oil. The threads on the carb for the needle valve seems to be worn & the needle is loose & the only thing I could do was wrap plumber tape on the threads. After awhile of flying the engine quits & dead stixs. When I look at the needle setting it seems to have changed. I don't have any ideas what else to do. OS doesn't have any parts available. Any help would be appreciated.
Old 07-20-2007, 10:23 AM
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Default RE: OS FS40 4 Stroke

If the needle settings are changing in flight, you'll need to find a way to stop them from vibrating into different settings. O.S. puts a ratchet spring on the needle valve assembly for just that purpose. The one for your engine is no longer available, though. You may have to go to one of the online sales areas, such as the RCU Marketplace to find a new carb or needle valve assemby.
Old 07-22-2007, 10:51 AM
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Default RE: OS FS40 4 Stroke

Bax, thanks for the answer. Can the threads be worn on the needle valve causing the change. If I push or pull on the needle valve I can hear a change in rpm's. Also I changed to a OS K plug but when I pull off the ignighter the engine runs rougher. I think the best thing is to take the carb apart & clean everything since it has been sitting for a number of years. What about seals & 'o' rings on the carb & where it mounts to the head & block. Thanks again
Old 07-23-2007, 09:56 AM
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Default RE: OS FS40 4 Stroke

If you can wiggle the needle and the mixture changes, then the fit is worn out. You can sometimes alleviate this by putting a piece of fuel tubing on the threaded part to apply some pressure. It also acts as a gasket to help keep out air. Some engines has this installed when new.

As far as o-rings go, they really don't wear out. If they are not hard and stiff, or cut, they're OK.
Old 10-17-2007, 07:50 PM
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Default RE: OS FS40 4 Stroke

I've installed a small piece of fuel tubing over the needle valve to hold it in place and to seal the NV from leaks.

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